Preheat oven to 350°F Spray three 8 inch cake pans with baking nonstick spray. Place an 8 inch parchment paper on the bottom. Spray again.
Using a blender, blend 15 biscoff cookies into a fine crumb. In a mixing bowl, mix the flour, biscoff crumbs, baking powder, and salt.
15 Biscoff cookies, 2 ¾ cup All-purpose flour, 2 ¼ teaspoon Baking powder, 1 ½ teaspoon Salt
Using a mixer, beat the butter, oil, and sugar. Beat on high for 3 minutes it will be very light and fluffy. Add in vanilla, sour cream, and eggs. Beat on high for 2 minutes until fluffy.
1 cup Unsalted butter, ⅓ cup Oil, 1 ¾ cup White granulated sugar, 1 tablespoon Pure vanilla extract, ⅓ cup Sour cream, 4 Large eggs
Add in ⅓rd of the dry ingredients and half of the buttermilk. Mix until almost combined. Add in another ⅓rd of the dry ingredients and the rest of the buttermilk. Finish with the rest of the dry ingredients. Take bowl off the mixer and scrape the bowl.
1 ¼ cup Buttermilk
Pour the batter evenly through the three cake pans. Bake for 28-35 minutes. Bake until a toothpick inserted comes out clean.
Let the cakes sit for 10 minutes in the hot pans. Transfer the cakes to a cooling rack. Let the cool completely before decorating.