Brownie in a Mug

Place butter, sugars, and salt in a mug. Microwave for 20 seconds until butter is melted but not boiling.

Remove from microwave, stir well to combine, and whisk in egg. Add vanilla and water.

Mix in flour, cocoa powder, and chocolate chips, saving a few for garnish. 

Garnish with remaining chocolate chips, marshmallows, sprinkles, and malt balls. 

Microwave for 45 seconds; do not overcook. Let cool and eat immediately.