Preheat your oven to 350°F (175°C) and grease or line an 8x8 inch baking pan with parchment paper.

In a medium bowl, whisk together the melted butter and granulated sugar to create a smooth, glossy mixture.

Add lemon zest and juice, then stir to combine.

Crack in the eggs, one at a time, blending well after each addition. Add vanilla extract and mix.

In another bowl, combine the flour, baking powder, and salt. Gradually mix the dry ingredients into the wet mixture until just combined.

Spread the batter evenly into the prepared baking pan.

Bake for about 20-25 minutes, or until a toothpick inserted in the center comes out clean or with a few moist crumbs.

Cool in the pan on a wire rack before dusting with powdered sugar.