Preheat oven to 350 degrees F (175 degrees C).

Grease a 9 inch square baking pan.

In a large bowl, combine the flour, baking powder, salt, sugar and unsweetened cocoa.

Stir in the oil, vanilla, and 3/4 cup of evaporated milk until well blended.

Spread the mixture evenly into the prepared pan.

Bake for 25 to 30 minutes in the preheated oven, until a toothpick inserted into the center comes out clean.

To make the frosting: In a small saucepan, combine the remaining evaporated milk, sweetened cocoa, and butter.

Cook over medium heat until almost boiling, remove from heat and chill until brownies are ready.

When brownies are completely cool, frost with the chilled icing and cut into bars, or frost them individually.