Preheat the oven to 180°C (350°F). Grease and line two 8-inch round cake pans.
In a bowl, sift together the flour, baking powder, baking soda, and salt. Set aside.
In a large mixing bowl, beat the sugars and oil together until combined.
Add eggs one at a time, then stir in vanilla and melted Biscoff spread.
Alternate adding the dry ingredients and milk into the wet mixture. Mix until smooth.
Divide the batter evenly between the pans.
Bake for 28–30 minutes or until a toothpick inserted comes out clean.
Cool the cakes in the pan for 10 minutes, then remove and let them cool completely on a wire rack.
For the frosting, beat butter until light and fluffy. Add powdered sugar gradually, then mix in Biscoff spread. Add milk if needed.
Frost and assemble the cake. Sprinkle crushed Biscoff cookies on top. Chill slightly before serving for best texture.