Preheat oven to 325°F. Spray mini muffin tins with nonstick cooking spray.

Beat butter, shortening, and cream cheese with an electric mixer on medium to high speed for 30 seconds. Add brown sugar, baking powder, and salt. Beat until combined, scraping sides of bowl occasionally. Beat in egg and vanilla. Mix in flour gradually.

Chill dough if too sticky for 30-60 minutes, otherwise continue.

Shape dough into 36 balls (~1 1/4 inches). Press into the bottoms and sides of muffin cups.

Prepare the filling: melt chocolate and butter over low heat. Remove from heat, then stir in egg, brown sugar, vanilla, and peppermint extract. Spoon about 1 teaspoon into each dough-lined muffin cup.

Bake for 15-20 minutes until crust is firm and filling is puffed. Cool in muffin cups for 5 minutes, then transfer to wire rack to cool completely.

Make ganache: heat heavy cream until boiling, pour over chopped chocolate, let sit 5 minutes, then stir until smooth.

Top each cooled tart with ganache and sprinkle crushed peppermint candies.