Preheat the oven to 350°F (180°C). Spray two *8-inch cake pans with non-stick spray and line the bottoms with circles of parchment paper.
Sift all purpose flour into a mixing bowl and add white granulated sugar, baking soda and salt. Mix together.
Prepare your homemade buttermilk by adding 1 tablespoon of lemon juice to a measuring jug and then adding room temperature milk up to the 1 cup line. Let it curdle for a few minutes.
Add the buttermilk, eggs, melted biscoff cookie butter, canola oil and vanilla extract and mix into a batter. Don't over-mix.
Transfer the batter to your two prepared 8-inch cake pans.
Bake for 30 minutes or until a toothpick inserted into one of the cakes comes out clean.
Allow the cakes to cool in the pans for a few minutes before removing them from the pans and transferring to a wire cooling rack to cool completely before frosting.
Prepare your frosting by adding softened butter and biscoff cookie butter to your stand mixer and beating together until smooth and creamy.
Add powdered sugar and milk and beat again until fluffy.
When the cakes are completely cool, frost with biscoff buttercream.
Decorate by drizzling melted biscoff cookie butter over the top and sprinkling some crushed biscoff cookies.
Refrigerate the cake for 1 hour for the frosting and biscoff drizzle to set and then slice and serve.