Preheat the oven to 350°F (175°C) and grease a baking pan.
In a bowl, mix melted butter and sugar until combined.
Add eggs, lemon juice, and lemon zest, and mix well.
In another bowl, whisk together flour, baking powder, and salt.
Gradually add the dry ingredients to the wet mixture and stir until just combined.
Pour the batter into the prepared baking pan and spread evenly.
Bake for 20-25 minutes or until a toothpick comes out clean.
While the brownies cool, prepare the cream cheese frosting by beating cream cheese, powdered sugar, and milk until smooth.
Spread the frosting over the cooled brownies and cut into squares.