For the crumble: Brown the butter over medium heat. Stir with a whisk. Once golden brown, remove from the heat immediately. Be sure to not burn it! Add the flour, brown sugar, salt and cinnamon, and continue to heat until fully combined.
For the cupcakes: Preheat the oven to 345 degrees F. Line cupcake pans with 15 liners.
Combine the flour, baking powder, baking soda and salt in a medium bowl.
In a mixer with a paddle attachment at medium speed, combine the butter and brown sugar. Mix until fully combined. One ingredient at a time, add the bananas, sour cream, vanilla and eggs, mixing well between additions.
Add the dry ingredients to the bowl and continue to mix. Do not over mix! Scoop the batter into the cupcake liners and add a generous amount of brown butter crumble on each top. Bake for 12 to 15 minutes. Check for doneness by inserting a toothpick into the cupcakes. If it comes out clean, they are done. Allow to cool.
For the buttercream: In a mixer with a paddle attachment at medium speed, blend the speculoos until smooth. Add the butter and mix until fully combined. Add the powdered sugar until you reach a smooth, silky consistency.
To assemble: Place the speculoos buttercream in a piping bag with a plain tip and pipe to your hearts content. There is no wrong way, have fun and enjoy!
This recipe was created by a contestant during a cooking competition. It has not been tested for home use.