Oh my goodness, friends, are you in for a treat today! Literally :). My Lemon Bar Sheet Cake with Lemon Curd and Shortbread Crust is the PERFECT bite of zesty lemon all round with a bit of shortbread to give you that lemon-bar feeling. Although this cake has a couple extra steps, it’s still easy to throw together, and even more fun to decorate. This is such a bright and happy cake for spring and even (dare I say) summer, but can be enjoyed year round!

Meet my newest cake for my Sheet Cake Pan Series I’ve been sharing this month. 3 cakes down, and only a few more to go! I hope sharing these cakes in an easy 9×13 form encourages bakers from all levels to start making these delicious cakes without having to worry about any kind of stacking if that’s not in your comfort level quite yet.

Original Lemon Bar Cake Recipe

Yes, this cake certainly looks familiar to a few of you! My Lemon Bar Cake is one I have loved for so long, and the recipe is right here. When I asked you on my Instagram page which cakes of mine you’d like to see transformed into a sheet cake in this sheet cake series, SO MANY of you said lemon cake and lemon bar cake. So your wish is coming true here today, and I’m so glad we went with this one. It’s an instant hit, and is the perfect combination of beautiful textures in each and every single bite.

LEMON CURD HEAVEN

I’ve shared this recipe before in my Cake Confidence cookbook with my Lemon Meringue Cake (which is oh-so-heavenly!). The lemon curd pairs beautifully with this cake, and highlights one of my favorite part of the classic lemon bar: that gooey zesty filling. Lemon curd may sound a touch intimidating if you’ve never made it before, but I promise you it’s worth it to make it up the day before you assemble (so it can fully set). It’s super easy to make, and here’s what you’ll need…

How to make the best homemade lemon curd

You’ll need only a few ingredients for my lemon curd. You will need a lemon zester and a way to get lemon juice out of your lemons. However, if you’re using pre-squeeze lemon juice, that works, too!

  • Lemon Juice – freshly squeezed is best, but pre-squeezed is fine from the store.
  • Lemon Zest – I love using a lemon zester, but you can use the tiniest holes on the side of a cheese grater if you need to. Just don’t zest down too far. You can strain out the zest at the end of making your curd if you’d like. I leave it in, personally.
  • Granulated Sugar – just a little. Er…. 3/4 cup. haha
  • Egg Yolks & Egg – You can save the egg whites for a meringue or to toss into your scrambled eggs later.
  • Butter – I used unsalted, and make sure to add it when your curd is off the heat.

Start with egg yolks and one egg white and whisk them together in a pan with sugar, lemon juice, lemon zest. I love using fresh lemons for the lemon juice – you’re needing lemon zest anyway, might as well use the actual lemon ;). The key to a dreamy lemon curd that isn’t scrambled eggs is to stay and whisk while the curd is heading up. When it thickens up, add in the butter a tablespoon at a time off the heat. It should thicken up beautifully. This is the time where you get to decide if you want the little pieces of zest in there or not. I usually strain it, but it still works out fine if you don’t. Like I said before, make this the day before while your cakes are baking (baking day is always separate than assembly day).

THE PERFECT SHORTBREAD COOKIE crust

For this cake, it starts off with my shortbread crust. This is made with Sandies cookies! They are darling little shortbread cookies by Keebler and you can find them near the Oreos in the cookie section, usually. My goodness, they are so buttery and soft and are absolutely perfect for this cake. It echoes the crust typically found on the bottom of the classic lemon bar. If you can’t find them, that’s okay!

You may use a different kind of shortbread cookie if you can’t find these specific ones, but make sure you have around 3 cups worth so that the rest of the ingredients work out well for the crust. Pulse the cookies into a fine powder, stir them up with the melted butter and a pinch of salt, then spread it flat onto your sheet pan. This crust presses down beautifully; better than any of my other crusts. It is hard to not sneak a few bites of it before pressing it down into the sheet pan, that’s for sure!

the best lemon cake

Classic lemon cake shouldn’t be hard. It should taste dynamite, but not have to slave away carefully measuring out flour and everything to make it happen. This is why I’ve perfected the doctored cake mix version of the classic yellow cake. Yes, it uses a cake mix, but before you run away, let me tell you that adding in the ingredients I do will make this YOUR FAVORITE LEMON CAKE of all time. You will forever use it as a base to any lemon cake combo you want to tackle in the kitchen. Use that lemon cake mix (any brand will do, I just prefer the taste of Duncan Hines) as your pre-measured dry ingredients, then add in your money ingredients: buttermilk, sour cream, eggs, oil, vanilla, and for that extra lemon flavor add in a whole lemon’s worth of lemon zest. THEN add in a touch of lemon extract if you’re a die-hard lemon lover like we are!

Add your cake batter right onto your crust. No pre-baking required. Just spread the batter onto the prepared sheet cake. It will bake flat, smell SO GOOD, and will be the perfect base for the cake decorations we’ll add on top… including that heavenly lemon curd!

Here’s a video of the process:

If you make one of my sheet cakes, I’d love to see it! Make sure to tag me @bakingwithblondie #bakingwithblondie so I can join in on all the fun!

Happy Baking!

xx, Mandy

Get the Recipe: Lemon Bar Sheet Cake with Lemon Curd and Shortbread Crust

5 from 3 votes
A Luscious Lemon Bar Sheet Cake with a zesty homemade Lemon Curd, Shortbread Crust on bottom, and a tasty lemon buttercream.
Servings: 15 Large Square Slices
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Ingredients
 

Lemon 9×13 Sheet Cake with Shortbread Crust

  • 3 cups shortbread cookie powder (11-15oz pulsed into a powder and then 3 cups measured out)
  • 5 Tablespoons unsalted butter , melted
  • 1 pinch salt
  • zest of 1 fresh lemon (about 1 Tablespoon)
  • 3/4 cup buttermilk, room temperature
  • 2/3 cup sour cream, room temperature
  • 3 whole eggs, room temperature
  • 1 egg white, room temperature
  • 1 Tablespoon vanilla
  • 1 teaspoon lemon extract, optional
  • 1/3 cup vegetable oil
  • 1/4 cup all purpose flour
  • 1 15.25oz Box Lemon Cake Mix (Duncan Hines is preferred)

Lemon Curd

  • 3 egg yolks
  • 1 whole egg
  • 3/4 cup granulated sugar
  • 1/2 cup lemon juice
  • zest of 2 lemons (about 2 Tablespoons worth)
  • 4 Tablespoons unsalted butter

Lemon Buttercream

  • 1 1/2 cup unsalted butter, left out of fridge for 15 minutes or so1 teaspoon lemon extract
  • 1  Tablespoon vanilla
  • 1 pinch salt
  • 1 teaspoon lemon extract, I used PK Lemon Drop Elixir
  • 1/4 cup heavy cream
  • 6-7 cups powdered sugar
  • 1 drop yellow gel coloring

Shortbread Crumble

  • 1 cup shortbread cookies, crumbled to sprinkle on top

Equipment

  • 9×13 sheet cake pan
  • Wilton 1M piping tip
  • Offset Icing Spatula or Cake Scraper
  • Lemon Zester/Juicer
  • Piping Bag or squeeze bottle for curd
  • food processor

Instructions
 

Lemon Cake with Shortbread Crust

  • Prep a 9×13 sheet pan with a swipe of shortening and dust of flour to prevent sticking. Preheat the oven to 325 degrees. Set aside.
  • For the crust, pulse about 15oz cookies into a powder, then measure out 3 cups into a bowl. Add in melted butter and salt, and stir until all the butter has been incorporated into the cookie powder for a fine crust.
  • Press the crust into the prepared 9×13 sheet pan and flatten evenly with the bottom of a glass or flat measuring cup. Set aside. There's no pre-bake needed.
  • For the cake, hand-whisk together all the ingredients except for the cake mix. Sift in the cake mix, and gently stir until incorporated. Pour directly onto the shortbread crust and bake for 28-30 minutes. Let cool in the pan completely before adding on the decoration. Make the curd while the cake is baking.

For the Lemon Curd

  • In a medium saucepan over medium heat, stir together the yolks, sugar, juice, and zest. Whisk together as the mixture begins to thicken, about 6 minutes. Curd should be thickening, and will be thick enough to coat the back of a spoon.
  • Remove curd from the heat, and stir in the butter cubes. Stir to combine until the butter has melted. Strain the curd, and discard the zest.
  • Cover the curd with a light layer of plastic wrap placed directly on top of the surface of the curd, and then store in the fridge until cooled. You’ll want it cold before adding it to your cake.

Lemon Buttercream

  • In a stand mixer fitted with a paddle attachment, whip up butter for about a minute until light and fluffy. Scrape down the sides of the bowl.
  • Add in salt, lemon extract, vanilla, almond extract, and heavy cream until combined. Slowly add in powdered sugar, about a half cup at a time. Add in the lemon yellow gel coloring. Add in more heavy cream if needed for a thinner consistency. Whip on high for a minute to create a soft buttercream, then back down to low for 30 seconds to beat out any air bubbles.

Assembly

  • Add 1 1/2 cups of buttercream to a piping bag fitted with a 1M piping tip, set aside.
  • Spread on the rest of the buttercream in a flat layer on top of the 9×13 cake. Use an offset icing spatula or cake scraper to make a flat, even layer.
  • Pipe on long lines of buttercream shells in a straight pattern.
  • Fill between the pattern with the lemon curd (you'll have a little extra, depending on how much curd you use).
  • Sprinkle on the crumbled shortbread on top. Enjoy!