Preheat oven to 350ºF. Grease or line a 8x8 baking pan with parchment paper.
Melt butter and let cool.
In a large bowl, whisk the eggs. Add the sugar and whisk together until light and lemon colored.
Add the lemon zest, juice, and butter, and whisk to combine.
Add flour and baking powder, whisking until just combined.
Pour batter into the prepared baking pan.
Bake in the center of the oven for 15 minutes, until the edges are set and a toothpick inserted into the center comes out clean.
Remove from oven and let cool.
While the brownies cool, combine the glaze ingredients in a bowl.
Drizzle over brownies and let glaze set for several minutes. Cut into squares and enjoy.