Preheat your oven to 350°F (175°C).

Grease a 9x9-inch baking pan with butter or cooking spray, or line it with parchment paper.

In a large mixing bowl, whisk together the gluten-free flour, granulated sugar, cocoa powder, baking powder, and salt.

In a separate bowl, mix the melted butter, eggs, and vanilla extract until smooth.

Pour the wet ingredients into the dry ingredients and stir gently until just combined.

Fold in chocolate chips or chopped nuts if using.

Spread the brownie batter evenly in the prepared baking pan.

Bake for 25-30 minutes, checking for doneness with a toothpick.

Let the brownies cool in the pan for about 10 minutes before transferring to a wire rack to cool completely.