In a microwave-safe mug, whisk together the flour, sugar, cocoa powder, baking powder, and salt until well combined.
Add the milk, vegetable oil, and vanilla extract to the mug. Stir until the batter is smooth and lump-free.
Gently fold in the white, milk, and dark chocolate chips, ensuring they are evenly distributed throughout the batter.
Microwave on high for 2 minutes, or until the cake has risen and is set in the center. Let it cool for a couple of minutes.
Generously top with whipped cream.
If desired, garnish with chocolate shavings.
Enjoy this decadent, single-serving Triple Chocolate Mousse Marvel!