1. Preheat your oven to 350°F (175°C). Grease an 8×8-inch baking pan or line it with parchment paper for easy removal.
2. In a large mixing bowl, whisk together the flour, sugar, baking powder, and salt until well combined.
3. In a separate bowl, mix the melted butter, eggs, lemon zest, lemon juice, and vanilla extract.
4. Slowly pour the wet ingredients into the dry ingredients, stirring until just combined. Be careful not to overmix, or the brownies will be dense.
5. Pour the batter into the prepared baking pan, smoothing the top with a spatula.
6. Bake for 20-25 minutes, or until the edges are golden and a toothpick inserted into the center comes out clean.
7. Allow the brownies to cool in the pan for about 10 minutes before transferring them to a wire rack to cool completely.
8. Once cooled, dust with powdered sugar if desired, slice into squares, and serve.

Remember, cooking is about using your senses, as my abuela taught me — trust the aroma and the golden edges to guide you!