Preheat oven to 350°F / 177°C. Spray a mini muffin tin with non-stick cooking spray. Set aside.
Before getting started, be sure that you have unwrapped the candy kisses so they are ready to add to the brownie bites right after baking.
In the bowl of a standing mixer with the paddle attachment, beat the shortening, egg, and sugar until light and fluffy, about 2 minutes. Add peppermint extract and mix just until combined.
Add flour, cocoa powder, baking powder, and kosher salt to the mixer all at once.
Mix on low just until combined (do not overmix).
Use a 1 Tablespoon measure to scoop out dough and roll it into even balls. Drop dough balls into prepared spaces of the mini muffin tin.
Bake until the centers are rounded in the middle and the edges look firm (the centers should still be fairly soft), 10 to 12 minutes.
Remove the brownies from the oven and, working quickly, press a candy kiss inside each warm brownie.
Allow brownies to cool completely in the pan. (The candy kisses will melt and then the brownie bites will continue to firm up in the pan and will be easy to remove.)
Note: After the candy kisses have fully melted (5 to 10 minutes), go back and gently press down on the pointy caps to flatten them. This is optional, but will give the filling a smooth surface.
Store in a sealed container at room temperature. Serve within 2 days.