Preheat your oven to 350°F (175°C). Line an 8x8 inch (20x20 cm) baking dish with parchment paper, leaving some overhang for easy removal.

In a microwave-safe bowl, combine the butter and half of the chocolate chips. Microwave in 20-second intervals, stirring in between, until fully melted and smooth.

In a large mixing bowl, whisk together the sugar, vanilla extract, and eggs until the mixture is light and fluffy.

Slowly pour the melted chocolate and butter mixture into the egg mixture, whisking continuously until fully incorporated.

Sift the gluten-free flour, cocoa powder, baking powder, and salt into the wet ingredients. Gently fold the dry ingredients into the batter until there are no dry spots left.

Incorporate the remaining chocolate chips and, if using, the chopped nuts into the batter to distribute evenly.

Pour the batter into the prepared baking dish and spread it evenly with a spatula to ensure uniform thickness.

Place the dish in the preheated oven and bake for 25-30 minutes until a toothpick inserted into the center comes out with a few moist crumbs attached.

Allow the brownies to cool in the pan for 10 minutes. Then use the parchment paper overhang to lift them out and place them on a wire rack to cool completely.

Once cooled, slice the brownies into squares and serve.