In a microwave-safe mug (10–12 oz), mix flour, cocoa powder, sugar, salt, and baking powder until well combined.
Stir in milk, oil, and vanilla extract. Mix until the batter is smooth, scraping the sides and bottom of the mug.
Fold in chocolate chips or other add-ins if desired.
Microwave on high for 60 to 75 seconds until the cake rises and looks set. Avoid overcooking.
Let cool for 1–2 minutes. Top with ice cream, powdered sugar, or whipped cream and enjoy straight from the mug.
