In a stand mixer fitted with the paddle attachment, beat the softened butter on medium-high speed until it becomes light and fluffy. Add the granulated sugar and brown sugar, then cream the mixture together for about 3 minutes, until smooth and well incorporated.
Next, scrape down the sides of the mixing bowl with a spatula to ensure everything is evenly mixed. Add in the vanilla extract, followed by the eggs—adding one egg at a time and mixing thoroughly after each addition.
Once the wet ingredients are combined, add the all-purpose flour, cake flour, Biscoff cookie crumbs, salt, baking soda, and cornstarch. Mix on the lowest speed just until the ingredients come together—do not overmix the dough. Then gently fold in the dark and white chocolate chunks, still using the lowest speed or a spatula.
Using a medium cookie scoop (size #16), portion out the dough. For each portion, split the dough in half. Place one frozen Biscoff dollop in the center of one half of the dough, then place the other half on top. Press the edges together and roll gently to form a sealed cookie dough ball with the Biscoff hidden inside. Once all the cookies are stuffed and shaped, arrange them on a baking sheet and place them in the freezer for another 30 minutes. This additional chilling step helps the cookies hold their shape and prevents excessive spreading while baking.
While the dough chills, preheat your oven to 410°F (210°C). Once the oven is ready and the cookies are firm, transfer them to a parchment-lined baking sheet and bake for 14 to 18 minutes. The cookies should be golden on the edges but still gooey in the center. After baking, leave the cookies on the hot pan for 15 minutes. This allows them to finish setting without over-baking in the oven. Once set, transfer them to a wire cooling rack.
* For an extra Biscoff boost, drizzle the cookies with melted Biscoff cookie spread and/or sprinkle crushed Biscoff cookies on top*