Preheat your oven to 350°F (175°C). Prepare an 8x8-inch baking pan by lining it with parchment paper or lightly coating it with cooking spray, and set it aside.

In a large mixing bowl or the bowl of a stand mixer, cream together the softened butter, granulated sugar, and lemon zest until the mixture becomes light and fluffy. Gradually beat in the eggs, adding them one at a time and mixing well after each addition. Mix in the lemon juice until fully incorporated.

Gently fold in the all-purpose flour and baking powder until just combined, being careful not to overmix. Transfer the batter to the prepared pan, smoothing it out into an even layer.

Bake in the preheated oven for 20-25 minutes, or until a toothpick inserted into the center comes out clean. Allow the brownies to cool in the pan for 10-15 minutes.

While the brownies cool, prepare the glaze by whisking together the powdered sugar, lemon juice, and zest until smooth. Pour the glaze over the warm brownies, using a spatula to spread it evenly across the surface.

Allow the glazed brownies to cool completely before cutting them into 16 squares.