Preheat your oven to 350°F (175°C). Grease and line three 8-inch round cake pans with parchment paper.
In a medium bowl, whisk together the flour, baking powder, baking soda, salt, and ground cinnamon. Set aside.
In a large mixing bowl, beat the butter, Biscoff spread, granulated sugar, and light brown sugar until light and fluffy, about 3-4 minutes.
Add the eggs one at a time, beating well after each addition. Mix in the vanilla extract.
Add the dry ingredients in three parts, alternating with the buttermilk, starting and ending with the dry ingredients. Mix until just combined.
Gently fold in the crushed Biscoff cookies.
Divide the batter evenly among the prepared pans. Bake for 30-35 minutes or until a toothpick inserted into the center comes out clean.
Let the cakes cool in the pans for 10 minutes, then remove from the pans and transfer to a wire rack to cool completely.
In a small saucepan, heat the heavy cream until it just begins to simmer. Remove from heat.
Place the chopped white chocolate and Biscoff spread in a heatproof bowl. Pour the hot cream over the chocolate and Biscoff spread. Let sit for 2-3 minutes, then stir until smooth.
Allow the ganache to cool to room temperature, then refrigerate until thickened, about 1 hour.
In a large mixing bowl, beat the butter and Biscoff spread until creamy and well combined.
Gradually add the powdered sugar, one cup at a time, mixing well after each addition.
Beat in the vanilla extract. Add the heavy cream, one tablespoon at a time, until the frosting reaches a smooth and spreadable consistency.
Level the tops of the cake layers with a serrated knife if needed.
Place one cake layer on a serving plate or cake stand. Spread a layer of Biscoff ganache over the top. Repeat with the second layer.
Place the third cake layer on top. Apply a thin layer of Biscoff frosting over the entire cake to seal in the crumbs. Refrigerate for 30 minutes.
Apply the remaining Biscoff frosting evenly over the top and sides of the cake.
In a microwave-safe bowl, heat the Biscoff spread and heavy cream together in 15-second intervals, stirring until smooth and pourable.
Using a spoon, drizzle the Biscoff mixture over the edges of the cake, letting it drip down the sides. Pour some over the top and spread it out with an offset spatula.
Decorate the top of the cake with whole or crushed Biscoff cookies and Biscoff truffles if desired.
Refrigerate the biscoff cake for at least 1 hour before serving to allow the frosting and ganache to set.
Have Fun Baking!