Preheat your oven to 325 degrees F. Spray two 8-inch pans with non-stick cooking spray, line the bottoms with parchment and spray again. Set aside.
Place the Biscoff cookies in a food processor or blender and pulse until the cookies are finely ground and resemble flour.
In a medium-size bowl, combine the Biscoff crumbs, all-purpose flour, baking powder, baking soda, and salt. Whisk until the ingredients are well-blended.
In the bowl of a stand mixer fitted the paddle attachment, beat the butter and sugars on medium speed until light and fluffy. Add the eggs, one at a time, beating well after each addition.
With the mixer on low speed, add 1/3 of the dry ingredients and mix until combined. Slowly add half of the buttermilk and mix until incorporated. Continue alternating the flour and buttermilk until it has all been incorporated. Scrape down the sides of the bowl and slowly mix for another 20-30 seconds.
Divide the batter evenly among your pans and bake for about 35 to 40 minutes, or until a toothpick inserted in the center comes out with a few moist crumbs on it. Cool 10 minutes on a wire rack before inverting onto cooling racks to cool completely.