In a medium sized bowl, whisk together the sugar, cocoa powder and flour.

In a larger bowl, whisk together the cooled butter, eggs, and vanilla. Stir the dry ingredients into the wet with a wooden spoon.

Scrape the batter into the baking dish. Microwave 4-7 minutes on high, just until the brownies are "done" in the middle.

Let the brownies cook on a rack 5-10 minutes, then cut into squares and eat.