World’s Best 5-Ingredient Mug Brownie

In a small bowl measure out sugar, flour, and cocoa powder.

Add milk and butter to mug and microwave 30 seconds. The butter should be almost completely melted. While mug is in the microwave, whisk dry ingredients together. This will help break up lumps.

Pour milk and butter into the bowl with the dry ingredients. Whisk until combined, 30–60 seconds.
Pour mixture back into the mug, making sure to scrape the bowl.

Microwave for 60 seconds. Center should look a bit molten, but when you tip the mug, the brownie should not slide around. If brownie slides, microwave it in 5-second bursts until it stays still when tilted. Let cool for about 2 minutes before eating.