Prepare the Oven and Muffin Pan: Preheat your oven to 350°F (175°C). Lightly grease a mini muffin pan or line it with mini paper liners. This recipe makes about 12-15 brownie bites, depending on the size of your pan.

Melt the Butter and Chocolate Chips: In a microwave-safe bowl, combine the butter and semi-sweet chocolate chips. Microwave in 20-second intervals, stirring between each interval, until the chocolate and butter are melted and smooth. Set aside to cool slightly.

Mix the Wet Ingredients: In a large mixing bowl, combine the granulated sugar, brown sugar, eggs, and vanilla extract. Whisk until well blended and smooth.

Combine the Chocolate and Wet Ingredients: Pour the melted chocolate mixture into the sugar mixture. Stir well until fully combined.

Add the Dry Ingredients: In a separate bowl, whisk together the all-purpose flour, cocoa powder, baking powder, and salt. Gradually add the dry ingredients to the wet ingredients, folding gently until just combined. Be careful not to overmix, as this can make the brownies less tender.

Assemble the Brownie Bites: Spoon about 1 tablespoon of the brownie batter into each mini muffin cup. Press a chocolate square or truffle into the center of each cup, then add a small amount of batter on top to cover the filling.

Bake: Bake in the preheated oven for 12-15 minutes or until the edges are set and a toothpick inserted into the edge (not the center) comes out clean. The center may still be gooey due to the chocolate filling.

Cool and Serve: Allow the brownie bites to cool in the pan for 5-10 minutes, then transfer to a wire rack to cool completely. Serve warm for an extra gooey center, or at room temperature for a firmer texture.