Microwave Brownies

According to one online reviewer, " this is by far the easiest, fastest, and most delicious brownie recipe I've ever made." Place an ice cream ball on top.
Brush an 8-inch square, microwave-safe baking dish with non-stick cooking spray. Put the butter and cocoa powder in a large bowl suitable for a microwave oven. Cook in the microwave on high power until the butter melts, 30 to 90 seconds, depending on the power and size of your oven (check this every 15 seconds). Add the sugar and beat until smooth. Let the mixture cool slightly, then whisk with the eggs and vanilla. Add the flour. Place the dough in the prepared baking dish.Cook in the microwave on high power until the brownies are in the center, 4 to 7 minutes, depending on the power and size of your oven (after 4 minutes, check the dough every 15 seconds). Let the brownies cool in the pan on a wire rack for 10 minutes. Cut the brownies into 8 squares and serve.