Beat in sugar and salt. Add the vanilla. Mix in the melted butter.
Add the cocoa and flour using the low speed on mixer.
Pour into a microwave safe dish (8 x8 or a round cake pan -- your microwave time will depend on what you use.).
Microwave on high for 3 to 5 minutes on a turntable, preferably. Do not let the center get totally dry or it will be overcooked. I took mine out when there was just a small moist spot in the center, but next time I will probably let it bake for maybe 10 seconds less. It finishes cooking as it cools.
You can frost if you like, but I prefer my brownies unfrosted.