Preheat the oven to 350ºF. Line a 12-cup cupcake pan with cupcake liners. Set aside.
Add the butter and brown sugar to the bowl of a stand mixer fitted with the paddle attachment. Beat together at high speed until light and fluffy, 4-5 minutes. *Alternatively, use an electric hand mixer and a large mixing bowl.
Add the eggs to the bowl and beat at high speed until light and voluminous.
Combine the flour and baking powder and add it to the bowl. Beat on a low speed just until combined. *Do not overmix or your cupcakes will be dry.
Divide the cupcake batter evenly between the cupcake liners, filling each about ¾ full.
Place the pan on the center rack of the preheated oven. Bake for 18 minutes, or until the cupcakes have risen and are a pale golden brown. Transfer pan to a cooling rack and set aside to cool.
Briefly heat ¼ cup of Biscoff spread in the microwave - just until it’s a little runnier than usual.
Use a corer to remove the center from the cooled cupcakes. *Be careful not to push the corer all the way down through the bottom of the cupcakes. Add a teaspoon of Biscoff to each hole.
Cookie Butter Frosting
To make the buttercream, add the softened butter to the bowl of a stand mixer fitted with the paddle attachment. Beat on a medium speed for 2-3 minutes, until creamy. Add the powdered sugar ½ cup at a time. Once all the powdered sugar has been added, beat on medium speed for 2 minutes.
Add the Biscoff spread to the mixing bowl, increase the speed to medium-high, and beat for 5 minutes.
Add the boiling water and beat at low speed - this will change the buttercream to a smoother consistency.
Decorating
Transfer the buttercream to a piping bag fitted with a star tip. Pipe buttercream swirls on top of each cupcake.
Warm the remaining Biscoff spread in the microwave for a few seconds or until it is pourable. Drizzle the warm Biscoff spread over the cupcakes then add Biscoff cookies on top of each cupcake. Enjoy!
Store cupcakes in an airtight container in the fridge for up to 3 days. Unfrosted cupcakes may be frozen for up to 1 month.
Notes
We use soft brown sugar to add a touch of caramel flavor to the cupcakes since this is a great accompaniment to the cookie butter flavor. You can substitute with white sugar if that’s all you have. When properly baked, the cupcakes will have risen to the top of the cupcake liners, be a pale golden brown and will spring back when gently touched with a finger. To core the cupcakes you can use a cupcake corer, sharp paring knife or we have found an upturned piping nozzle to be the perfect size and sharp enough to remove the sponge cleanly. We didn’t replace the piece of cupcake we cut away, as it can make the cupcake look a little lopsided. You can if you want to (or eat them!!). Adding boiling water to the Biscoff buttercream really smooths it out so that it is almost the consistency of a Swiss meringue buttercream. If you find the buttercream is too thin, you can add more powdered sugar, a tablespoon at a time. If it’s too thick, add extra boiling water a teaspoon at a time. We used a Wilton 1M piping nozzle to frost the cupcakes. Crush the Biscoff cookies up or add them whole as decoration (or a bit of both!)