Preheat oven to 350°F. In a large mixing bowl, whisk together melted butter, granulated sugar, and brown sugar until smooth. Beat in eggs one at a time, then stir in vanilla extract.

In a separate bowl, sift together flour, cocoa powder, and salt. Gradually add dry ingredients to the wet mixture, stirring until just combined. Fold in chocolate chips and nuts if using.

Spoon batter into the prepared mini muffin tin, filling each cup about 3/4 full.

Bake in preheated oven for 12-15 minutes or until a toothpick inserted into the center comes out with a few moist crumbs. Avoid overbaking to maintain fudginess.

Allow brownie bites to cool in the pan for 10 minutes before transferring to a wire rack to cool completely.

Once cooled, decorate with icing, sprinkles, or edible glitter to add a festive touch. Serve on a decorative platter for a party-ready presentation.

Store leftover brownie bites in an airtight container at room temperature for up to 3 days. For longer storage, freeze the bites in a single layer and then transfer to a zip-top bag.