- Preheat your oven to 350°F (175°C) and grease a mini muffin tin or line it with mini cupcake liners. 
- In a large mixing bowl, whisk together the flour, sugar, cocoa powder, baking powder, and salt until well combined. 
- In another bowl, mix the melted butter, eggs, and vanilla extract until smooth. 
- Pour the wet ingredients into the dry ingredients and stir until just combined. If using, fold in the chocolate chips and/or chopped nuts. 
- Spoon the batter into the prepared mini muffin tin, filling each cup about 2/3 full. 
- Bake in the preheated oven for 10-12 minutes or until a toothpick inserted in the center comes out with a few moist crumbs. 
- Allow the brownie bites to cool in the pan for 5 minutes before transferring them to a wire rack to cool completely.