Preheat your oven to 325 degrees F. Spray a 10-cup bundt pan with nonstick spray, dust well with flour, and 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. Continue to beat the batter for about 2 minutes on medium-high.
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.
Pour half of the batter into the bundt pan. Drizzle about 1/2 cup melted Biscoff spread over the cake batter. Pour in the remaining batter. Bake for 45 to 50 minutes. Cool completely in the pan before inverting onto cooling racks to cool completely.