Preheat oven to 375˚F. Coat a 6-cup standard muffin tin with cooking spray.
Add cereal to a food processor and process until it is the consistency of fine crumbs, about 1 to 2 minutes.
Transfer cereal to a medium mixing bowl.
Melt butter in microwave in a microwave-safe dish.
Add melted butter and sugar to the mixing bowl. Stir until well-combined.
Add a heaping ¼ cup of the cereal mixture to five of the muffin cups. Press evenly on the sides and bottom to form a cup.
Bake for 8 to 10 minutes or until set. Remove from the oven and cool on a wire rack for 30 minutes.
To make the filling, blend the raspberries and yogurt in a food processor until smooth, about 45 seconds. Transfer to a small bowl, cover, and refrigerate until ready to use.
Remove the cereal cups by inverting the pan on a flat surface and tapping on the bottom of each of the muffin cups so they pop out in one piece.
To serve, fill each cereal cup to the brim with the fruit mixture. Garnish with sprigs of mint, if desired.