In a large mixing bowl, beat the butter, light brown sugar, and granulated sugar until light and fluffy.
Add the eggs, one at a time, beating well after each addition.
Mix in the Biscoff spread until well combined.
In a separate bowl, whisk together the flour, cocoa powder, baking powder, baking soda, and salt.
Gradually add the dry ingredients to the wet mixture, alternating with the milk. Mix in the vanilla extract.
Divide the batter evenly among the cupcake liners.