Preheat the oven to 180C (350F). Line the baking form with the cupcake liners and put aside.
Put the butter and sugar in the bowl of a standing mixer. Mix them on a high speed until light and creamy.
Add the eggs, one by one, mixing after each addition. The batter will become a bit lumpy, but that's completely normal.
Soften the Lotus Biscoff spread in the microwave to make it more liquid. Add to the batter, together with the sour cream and vanilla extract. Mix until combined.
Sieve the flour, baking powder, and salt in a small bowl. With the mixer on a low speed, add the flour mixture to the batter, spoon by spoon, mixing after each addition.
Using an ice cream scoop, divide the batter evenly between the cupcake cases until each one is a bit over half-filled. Bake for 15-20 min, or until the toothpick inserted in the middle of the cupcake comes out clean with just a few crumbs on it. Leave on the side to cool down completely.
Now, start with making the Lotus Biscoff Mascarpone buttercream. Place the mascarpone cheese, butter, softened Lotus Biscoff spread, vanilla extract, and salt in the bowl of your mixer. Mix on high speed until completely smooth. Turn the mixer speed to low, and mix in the icing sugar, adding it gradually, spoon by spoon. In the meantime, place the Lotus Biscoff cookies in a plastic zip bag and crush them using a rolling pin. Using a spatula, fold the cookie crumbs into the mascarpone buttercream.
Pipe the mascarpone buttercream on top of the cupcakes and decorate with Lotus Biscoff cookies.
