01 - In a large microwave-safe mug (12–14 oz), whisk together all-purpose flour, cocoa powder, granulated sugar, baking powder, and salt until thoroughly blended.
02 - Pour in milk, vegetable oil or melted butter, and vanilla extract. Stir until batter is smooth and free of lumps.
03 - Fold in chocolate chips if desired.
04 - Microwave on high for 60 to 90 seconds until the cake rises and is just set in the center. Avoid overcooking.
05 - Allow to cool for 2 minutes. Top with whipped cream or ice cream if preferred, and enjoy directly from the mug.