Preheat your oven to 350°F (175°C). In a medium bowl, combine crushed Biscoff cookies, melted butter, brown sugar, and ground cinnamon. Mix until resembling coarse crumbs. Spread onto a lined baking sheet and bake for about 10 minutes until golden and fragrant. Let cool.

Grease and line three 8-inch round cake pans with parchment paper. Whisk together flour, baking powder, baking soda, and salt in a large bowl.

Cream together unsalted butter, Biscoff cookie butter, granulated sugar, and brown sugar until light and fluffy. Add eggs one at a time, mixing well. Blend in sour cream or yogurt, followed by alternating the flour mixture and buttermilk until just combined.

Distribute a portion of the Biscoff crumble into each pan, followed by equal spooning of cake batter. Reserve some crumble for topping. Swirl remaining crumble into batter’s surface.

Bake in the preheated oven for 30-35 minutes, or until a toothpick comes out clean. Allow layers to cool in pans for about 10 minutes, then transfer to a wire rack.

Heat heavy cream, Biscoff cookie butter, and corn syrup in a saucepan until simmering. Remove from heat, pour over chocolate chips, let sit for a minute then stir until smooth. Allow it to cool and thicken.

Beat together room temperature butter, cream cheese, and cookie butter until creamy. Gradually add powdered sugar and a splash of heavy cream, mixing until smooth and spreadable.

Pipe a ring of frosting around the bottom layer’s edge, fill center with ganache, and repeat for the second layer. Apply a thin crumb coat around the entire cake and chill for about 20 minutes.

Melt remaining cookie butter in the microwave, drizzle over the top of the chilled cake. Finish with frosting swirls and optional Biscoff truffles or crumbles.