In a large mixing bowl, cream together butter and sugar until light and fluffy, about 2-3 minutes. Add egg and vanilla extract, mixing until well combined.

In a separate bowl, whisk together flour, baking powder, and salt. Gradually add the dry ingredients to the wet mixture, stirring until just combined. Cover and refrigerate the dough for one hour.

Preheat your oven to 325°F (163°C) and adjust the oven rack to the center position.

Grease a mini muffin pan and drop rounded tablespoons of dough into each well, pressing the dough into the bottom and up the sides to create a slight indentation. Chill for 15 minutes.

Bake the cookie cups for 20-21 minutes, or until lightly golden. Press down the centers gently, creating a well for the filling. Cool in the pan for 5 minutes before transferring to a wire rack.

In a medium bowl, whisk together pudding mix and cold milk until thickened and smooth, about 2 minutes. Set aside to firm up slightly.

In a small saucepan, heat heavy whipping cream until hot but not boiling. Remove from heat and add chocolate, stirring until smooth to create a ganache.

Once cooled, fill each cookie cup with the pudding mixture and drizzle the warm ganache over the top. Let sit to set before serving or refrigerating.