Combine Biscoff crumbs, brown sugar, melted butter, and cinnamon in a bowl. Stir until well mixed and set aside.

Preheat your oven to 350°F. Grease and line the bottom of three 8-inch round cake pans.

In a bowl, whisk together flour, baking powder, baking soda, and salt.

With an electric mixer, beat the butter on medium speed for 3 minutes. Add the cookie butter and oil, mixing until combined.

Add granulated sugar and brown sugar, beating until creamy, about 2 minutes.

Add eggs one at a time, ensuring each is well mixed before adding the next. Stir in the sour cream.

Gradually mix in half the buttermilk, then half the flour mixture, followed by the remaining buttermilk and flour mixture until smooth.

Sprinkle 3 tablespoons of Biscoff crumble into each greased cake pan. Divide the batter among the pans, sprinkle more crumble on top, and gently swirl it into the batter with a spatula.

Bake for 30-35 minutes or until a toothpick comes out clean. Cool completely.

In a small pan or microwave-safe bowl, combine cookie butter, heavy cream, and corn syrup. Heat until hot and bubbles appear, then pour over the chocolate. Whisk until smooth.

Let it cool to room temperature. Blend with an immersion blender for 45 seconds for a smooth finish.

Cover and refrigerate for at least 2 hours or overnight.

Beat butter and cream cheese together for 2-3 minutes. Add cookie butter and mix for another minute.

Gradually add powdered sugar and 2 tablespoons heavy cream, mixing on low until combined. Increase speed to medium-high and beat for 2 minutes. Adjust with more heavy cream or powdered sugar for desired consistency.

Place a cake layer on a plate and pipe a ring of frosting around the edges. Fill the center with ganache.

Add the next layer and repeat the frosting and ganache filling.

Place the final cake layer on top. Spread a thin crumb coat of frosting over the cake, smooth it out, and chill for 30 minutes.

Apply a generous amount of frosting, smoothing the sides and top with a spatula or cake scraper.

Decorate with remaining Biscoff crumbs and pipe additional frosting on top if desired. Optionally, top with Biscoff truffles.

Store in the fridge for up to 5 days or freeze for up to 1 month. Use an airtight container for best results.