Step 1: Melt the butter and chocolate in the microwave for 1 minute. Set aside to cool.
Step 2: Add flour and sugar to a small mixing bowl, and mix well.
Step 3: Beat the egg and milk thoroughly. Mix in the melted chocolate and vanilla essence.
Step 4: Mix this into the flour mixture. Pour the mixture into a large coffee mug (300 ml).
Step 5: Top with nuts or chocolate chips. Microwave for 2.5 minutes at high power (1000 watts).
Step 6: Keep aside for 3 minutes before plunging in.