Choose the right mug: Use a microwave-safe mug that holds at least 12 ounces. Lightly grease it with a dab of oil or butter to prevent sticking.
Mix the dry ingredients: Add flour, granulated sugar, brown sugar, cocoa powder, baking powder, and a pinch of salt to the mug.
Stir well to combine, breaking up any cocoa clumps.
Add the wet ingredients: Pour in milk, oil or melted butter, and vanilla. Stir until you have a smooth, thick batter with no streaks of flour.
Create the lava center: Sprinkle the chocolate chips or chopped chocolate over the batter. Gently press them into the center so they’re covered but not sunk to the bottom.
Microwave: Cook on high for 60–90 seconds.
Start checking at 60 seconds. The top should look set around the edges but slightly glossy in the middle for a molten center.
Rest briefly: Let the mug cake sit for 30–45 seconds. This helps the structure set while keeping the core gooey.
Finish and serve: Top with ice cream, a dollop of whipped cream, or a pinch of sea salt.
Enjoy straight from the mug while warm.