Preheat your oven to 350°F (175°C). Line three 8-inch round cake pans with parchment paper and spritz them with non-stick spray.

In a large mixing bowl, whisk together the all-purpose flour, granulated sugar, brown sugar, baking powder, ground cinnamon, and fine salt until combined.

Add softened unsalted butter to the dry ingredients and mix until coarse crumbs form. Gradually add egg whites, buttermilk, vegetable oil, and vanilla extract, mixing until smooth.

Distribute the batter evenly among the prepared pans and smooth the tops. Bake for approximately 33-35 minutes, or until a toothpick comes out clean.

Cool the cakes in the pans for about 10 minutes before transferring them to a wire rack to cool completely.

In a mixing bowl, beat softened butter until light and fluffy. Gradually add powdered sugar, mixing on low, then increase speed until well incorporated.

Add heavy whipping cream and mix until creamy and smooth.

In a separate bowl, gently fold cookie butter into a portion of the prepared vanilla buttercream until uniform.

Place one layer of cake on a serving platter. Spread a layer of vanilla buttercream on top and drizzle with warm cookie butter. Repeat with remaining layers.

Apply a thin crumb coat around the entire cake and chill for about 20 minutes. Finish with generous vanilla frosting and decorate with chopped Biscoff cookies.