Preheat your oven to 350°F (175°C). Grease a 9x13-inch baking pan or line it with parchment paper for easy removal.
In a large mixing bowl, combine the melted butter and granulated sugar. Whisk until well blended.
Add the eggs one at a time, mixing well after each addition. Stir in the vanilla extract.
In another bowl, whisk together the flour, baking powder, and salt. Gradually add the dry ingredients to the wet mixture, stirring until just combined.
Fold in the lemon juice and lemon zest until evenly distributed.
Pour the batter into the prepared baking pan and spread it evenly.
Bake for 20-25 minutes, or until a toothpick inserted in the center comes out clean.
Allow the brownies to cool in the pan for at least 30 minutes before dusting with powdered sugar and cutting into squares.