Preheat your oven to 350°F (175°C).

Prepare an 8x8-inch baking pan by greasing it or lining it with parchment paper.

In a separate bowl, whisk together the gluten-free all-purpose flour, baking powder, and salt.

In a large mixing bowl, combine the melted butter and granulated sugar. Stir until smooth, then add the eggs, fresh lemon juice, lemon zest, and vanilla extract. Whisk until creamy.

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

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

Bake for 20-25 minutes, checking for doneness with a toothpick.

Allow the brownies to cool in the pan for about 10 minutes, then transfer to a wire rack to cool completely. Dust with powdered sugar if desired, cut into squares, and serve.