In a microwave-safe mug, whisk together the all-purpose flour, cocoa powder, granulated sugar, and a pinch of salt until well combined.

Add the whole milk, vegetable oil, and vanilla extract to your dry ingredients. Stir until the mixture is smooth and there are no lumps.

Place your mug in the microwave and cook on high for approximately 1 minute, keeping an eye to prevent overflow.

Let your brownie cool for a minute before enjoying it straight from the mug or topped with ice cream.