Soft and zesty lemon sheet cake studded with fresh blueberries, slathered in lemon curd, and topped with blueberry buttercream and fresh lemons & blueberries – this cake has it all! It’s such a bright and flavorful cake, and the flavors will have you falling in love with all things lemon and blueberry with each bite.

Fresh Lemon Blueberry Sheet Cake

This cake comes together very quickly and uses very simple, but lovely, ingredients. As always, I love baking with a box mix and then doctoring it up to taste better than scratch! It’s a method bakers around the world love to do (as well as many bakeries!) and always yields the most perfect results. If you haven’t tried it yet, I strongly suggest you do – it’s been a go-to for me for many years and although I love baking from scratch, there’s nothing as soft and perfect as a cake made from a humble box mix (doctored up, of course).

Here’s what you’ll need for the lemon blueberry sheet cake (the full list of instructions is below with the recipe):

  • Fresh Lemon Zest
  • Lemon Box Cake Mix (I used Duncan Hines)
  • Fresh blueberries
  • Sour Cream – room temperature
  • Buttermilk – room temperature
  • Vanilla
  • Vegetable Oil
  • Eggs – room temperature

Combine the ingredients in a bowl and whisk together except for the cake mix. Sift in the cake mix, then fold to combine. Spread into a prepared sheet cake pan, then bake. (Full instructions are below with the recipe).

What Baking Pan Should I Use?

I’ve tried this recipe with metal, dark metal, and ceramic and they all baked up beautifully! Here’s a link to one that’s similar to the one you see in these photos: HERE.

How to make the very best 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 â€“ 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 â€“ just a little. Er…. 3/4 cup. haha
  • Egg Yolks & Egg â€“ You can save the egg whites for a meringue or to toss into your scrambled eggs later.
  • Butter â€“ I used unsalted, and make sure to add it when your curd is off the heat.

The detailed instructions are below with the directions. It can keep for up to a week at peak freshness and flavor. It can also be frozen if you need to make it far in advance.

Tools for lemon curd

There’s a couple tools I love that make this process much easier!

How to make easy blueberry buttercream

This is the EASIEST blueberry buttercream you’ll ever make, and it comes together beautifully. It starts with my vanilla buttercream base and adds in one ingredient to give it the most wonderful creamy blueberry flavor: blueberry emulsion!

I usually find my emulsions straight from the craft store locally, but you can also order it online here. The jar is around $7, but lasts for MANY cakes, fillings, and buttercream batches. You’ll also love adding it to your muffins, pancakes, etc. It’s quite versatile and I love the flavor.

Here’s the ingredients you’ll need for the blueberry buttercream:

  • Blueberry Emulsion
  • Unsalted Butter
  • Salt
  • Heavy Cream
  • Vanilla
  • Powdered Sugar
  • Heavy Cream

The directions are below. If you’d like the buttercream to be not as purple (the emulsion makes it purple), then you can add in a touch of blue gel coloring to add a little more of a vibrant blue to match the blueberries.

Assembly

This cake is easy peasy! Just bake the sheet cake, let it cool, spread on the lemon curd, place it in the freezer for 5 minutes to set the curd (so you can do the next step), spread on the buttercream, and top with the lemon slices and fresh blueberries!

Here’s a video of the process:

As always, I can’t wait to see you try this one. The taste is incredible and will become one you love making year after year! As always, if you make my cakes, I’d love to see it! Make sure to tag me @bakingwithblondie or #bakingwithblondie so I can join in on all the fun.

Happy Baking,

xo, Mandy

Get the Recipe: Lemon Blueberry Sheet Cake with Lemon Curd

The most gorgeous lemon blueberry sheet cake slathered with lemon curd and topped with silky blueberry buttercream.
Servings: 12 slices
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Ingredients
 

Lemon Blueberry Sheet Cake

  • 3/4 cup buttermilk , room temperature
  • 2/3 cup sour cream , room temperature
  • 3 large eggs, room temperature
  • 1/3 cup vegetable oil
  • 1 Tablespoon vanilla
  • zest of one lemon (about 1 Tablespoon)
  • 1 15.25oz Lemon Cake Box Mix, *Duncan Hines
  • 2 cups fresh blueberries

Lemon Curd (double batch) – there will be a little left over

  • 2 large eggs
  • 6 egg yolks
  • 1 1/2 cup granulated sugar
  • 1 cup lemon juice
  • 1/4 cup lemon zest
  • 1/2 cup unsalted butter

Easy Blueberry Buttercream

  • 1 1/2 cup unsalted butter, left out at room temperature for 10 minutes
  • 1 Tablespoon vanilla
  • 1 pinch salt
  • 1 Tablespoon Blueberry Emulsion
  • 1/2 cup heavy cream + more to thin if needed
  • 7-8 cups powdered sugar

Garnishes

  • Fresh Lemon Slices

Instructions
 

For the Lemon Blueberry Cake

  • Preheat the oven to 325 degrees (convection bake) and prep a 9×13 pan with a little baking spray or shortening + flour to prevent sticking. Set aside.
  • In a large bowl, hand whisk together all the ingredients except for the cake mix. Sift in the cake mix and fold in gently until combined. Don't overmix. Toss in the blueberries and gently fold them in. Spread the batter into the prepared baking dish. Bake for 25-27 minutes until the center is baked through. Set aside to cool completely.

For the Lemon Curd *Make in advance up to a few hours to overnight to set

  • In a medium saucepan over medium heat, whisk together the eggs, sugar, lemon juice, and zest until the mixture thickens, about 3-5 minutes (keep whisking! we don't want scrambled eggs!). Remove the curd from the heat and add in the butter, 1 tablespoon at a time. Strain the curd to remove the zest. Transfer to a container to store in the fridge for a couple hours to cool and thicken – I usually do mine overnight.

For the Easy Blueberry Buttercream

  • In a stand mixer fitted with a paddle attachment, whip up the butter until it's light and fluffy, then add in the vanilla, salt, and blueberry emulsion. Add in the heavy cream, then toss in the powdered sugar with the mixer on low speed. If it's too thick, add in a tiny bit more heavy cream. Turn the mixer up to high speed and whip up for 2 minutes until the buttercream is light and fluffy. Use a wooden spoon to beat out the air bubbles before adding to the cake.

Assembly

  • On the cooled cake, spread the cooled/thickened lemon curd in a flat layer. Place into the freezer for 5 minutes to firm up a bit. Pipe on the blueberry buttercream (I didn't use a tip, just a piping bag with the end snipped off), and then spread flat with an offset icing spatula. On one half of the cake, add on the lemon slices and blueberries for garnish/decoration. Enjoy!
Author: Mandy Merriman – Baking with Blondie