Preheat oven to 350°F. Generously grease a mini muffin pan (these don’t work in regular-sized muffin tins) with cooking spray.
Combine flour, cocoa powder, brown sugar, granulated sugar, baking powder, salt, and mini chocolate chips. Whisk to combine, then set aside.
Use a separate, small microwave-safe bowl to combine semi-sweet chocolate chips with butter. Microwave for 25 seconds, stir for 15 seconds, and return to the microwave for another 15 seconds. Remove and stir until smooth (return to the microwave another 15 seconds as needed until melted). The mixture will be thick. Stir until smooth and back to room temperature. Add egg and stir again until smooth.
Use a spatula to scrape all chocolate mixture into dry ingredients. Mix until completely combined. Keep stirring until you have a thick dough. Scrape edges of the bowl as needed, and don’t overmix.
Use a tablespoon measuring spoon to measure out dough and place in each mini muffin pan cavity. You should get 15 brownie bites. Open chocolate bar; there should be large squares. Cut each chocolate square into 4 smaller squares and gently place 1 square into the top of each cookie. Don’t press down much; it doesn’t need to be covered by dough. Bake 10–12 minutes, and be careful to not overbake.
Remove pan from oven and let stand 10–15 minutes or until firm enough to easily coax out of muffin pan. I use a small spoon and fork to gently pull them out. It’s okay if the middle sinks a little. Because we’re using a chocolate bar instead of chocolate chips (which are resistant to melting), the chocolate should stay soft and gooey for about 45 minutes after baking. If you want gooey leftovers, microwave any remaining cookies 5–10 seconds. If you like salty-sweet flavors, add a sprinkle of Maldon sea salt flakes to the top of these. Enjoy warm.
Notes
Note 1: Brownie Bites need Dutch-process cocoa powder instead of standard cocoa; read the post for my favorite or use Hershey’s® Special Dark cocoa powder.Storage: Store leftover brownie bites in an airtight container at room temperature for up to 3 days or in the fridge for up to a week. Warm slightly before serving for the best texture.