Preheat oven to 350°F.
In a medium bowl, mix together the melted butter and cocoa powder until smooth.
Add the flour, salt, and sugar then mix together. The mixture will be dry and crumbly.
Add in the eggs and vanilla extract and mix until smooth.
Line a 9x13 pan with parchment paper and pour batter into pan.
Bake for 20 to 25 minutes, or until a toothpick inserted in the middle comes out clean.
While the brownies are baking, make the frosting by whisking together the butter, milk, powdered sugar, cocoa powder, and vanilla extract. The frosting should be thick and spreadable. It should be similar to the consistency of canned frosting but way better. If it’s too thick add a little milk, a tablespoon at a time.
Let sit for 15 to 20 minutes before frosting. Then spread frosting over the top of the brownies.
Let cool completely before slicing.