Preheat your oven to 350°F (175°C) and grease a 9x13-inch baking pan or line it with parchment paper.

In a medium saucepan, melt the butter over low heat.

Remove from heat and stir in the sugar until well combined.

Allow the mixture to cool slightly before adding the eggs one at a time, mixing well after each addition.

Stir in the vanilla extract.

In a separate bowl, whisk together the flour, cocoa powder, baking powder, and salt.

Gradually add the dry ingredients to the wet mixture, stirring until just combined.

Fold in the chocolate chips.

Pour the brownie batter into the prepared baking pan and spread it evenly.

If using, sprinkle mini marshmallows on top of the batter.

Bake in the preheated oven for 25-30 minutes, or until a toothpick inserted into the center comes out with a few moist crumbs.

Remove from the oven and let cool in the pan for about 10 minutes.

Once cooled, lift the brownies out of the pan using the parchment paper and cut them into bite-sized squares.

Before serving, top the brownies with red and blue sprinkles.