In a microwave-safe mug, add flour, sugar, cocoa powder, baking powder, and salt. Mix well.
Add melted butter, milk, egg, and vanilla extract. Stir until smooth.
Place the chocolate chunk in the center of the batter.
Microwave the Chocolate Molten Lava Mug Cake for 1 minute 30 seconds.
If needed, cook for an additional 30 seconds.
The center should remain slightly gooey—do not overcook.
Let it cool for 5 minutes, then add toppings and enjoy.