1. Preheat the oven to 350°F and line a 12-cup muffin pan with cupcake liners.

2. In a medium bowl, whisk together the flour, baking powder, salt, and cinnamon.

3. In a large bowl, beat the softened butter, granulated sugar, and brown sugar until pale and fluffy.

4. Add the eggs one at a time, mixing well after each addition, then mix in the vanilla extract.

5. Add the sour cream and mix until combined.

6. Add the dry ingredients in three additions, alternating with the milk, and mix just until the batter is smooth.

7. Divide the batter evenly among the cupcake liners, filling each about two-thirds full.

8. Bake for 18 to 21 minutes, or until a toothpick inserted in the center comes out clean.

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

10. Use a cupcake corer or small knife to remove the center of each cooled cupcake.

11. Spoon or pipe Biscoff cookie butter into each cupcake center.

12. For the frosting, beat the softened butter until creamy, then mix in the Biscoff cookie butter.

13. Add powdered sugar gradually, then beat in heavy cream, vanilla extract, and salt until fluffy and pipeable.

14. Pipe or spread the frosting over the filled cupcakes.

15. Top with crushed Biscoff cookies and optional cookie halves before serving.