Preheat oven to 180°C.
Line an 8-inch square pan with baking paper.
Combine melted butter, sugar, and lemon zest in a medium bowl.
Whisk together well.
Whisk in the eggs very well.
Mix the lemon juice.
Sprinkle the flour, baking powder, and salt evenly over the bowl,
and stir to combine.
Spread the mixture in the prepared 8-inch pan.
Bake for around 25 minutes, until the edges are starting to crackle
and turn golden brown.
Remove brownies from the oven and let cool slightly.
To make the glaze: whick together the icing sugar, lemon juice, and lemon zest.
Pour over the brownies.