Preheat your oven to 160ºC (320ºF) and line a cupcake pan with cupcake liners.

In a large mixing bowl, combine the granulated sugar, dark brown sugar, all-purpose flour, baking powder, baking soda, and salt, whisking until fully mixed.

In a separate bowl, mix the sour cream and Biscoff spread until smooth, then add the whole milk, vegetable oil, eggs, and vanilla extract, blending until creamy.

Pour the wet ingredients into the dry mix, gently folding until no lumps remain, being careful not to overmix.

Distribute the batter among the prepared cupcake liners, filling each about two-thirds full, and bake for 20 to 23 minutes.

Let the cupcakes cool in the pan for about 5 minutes, then transfer them to a wire rack to cool completely.

Beat the butter until light and fluffy, then add Biscoff spread, powdered sugar, and a splash of milk, mixing to desired consistency.

Once cooled, frost the cupcakes with Biscoff buttercream using a piping bag and create a well in the frosting to drizzle melted Biscoff spread.

Sprinkle crushed Biscoff cookies on top for decoration and serve.