Prep two large aluminum cookie sheets with parchment paper and set aside
Preheat oven to 410 degrees.
In a stand mixer fitted with a paddle attachment, whip up the butter for 1 minute until it's light and fluffy, then add in the biscoff, sugars and then cream together for 3 minutes on high speed.
Scrape down the sides an add in the vanilla (if using), and eggs one at a time; whip up well between each addition.
Add in the flour, biscoff powder, cornstarch, baking soda, and salt (not the sea salt) and slowly mix together either by hand or on the very lowest speed. Do not overmix, but make sure everything is incorporated (especially all dry ingredients).
Reserve 1/8 cup of each size of chocolate chips, then stir in the rest of the chocolate chips gently into the dough. Split dough in eight balls and place 4 cookie dough balls on each cookie sheet. Hand press on the reserved chocolate chips, and sprinkle on the sea salt and biscoff crumbles. Make sure the add-ons on top are below the cookie dough line (or they will burn!).
Bake for 9-10 minutes. They should be slightly golden, thick, tall, and gooey in the center. Let cool on the pan for 1 minute, then transfer to a cooling rack for 10 minutes to finish setting up.