Preheat the oven to 350˚F and line a 9-inch square baking tin with foil, letting it hang over the sides a bit.
Cream the butter and sugar together, then add in the vanilla and eggs and mix again.
Add the cocoa powder and flour gradually, then transfer the batter into the baking dish.
Bake for about 20 minutes or until a knife inserted into the middle comes out with only a couple of moist crumbs.
While the brownies cool, mix the frosting ingredients to make the frosting.
Add more milk if it’s too dry or more powdered sugar if it’s too runny.
Spread the frosting over the brownies while they’re warm so some melts into them.
Lift the brownies out of the pan using the foil you let overhang the baking pan sides.
Cut into squares and serve.