Combine water, butter and essence in a large (1 cup capacity) coffee mug. Add remaining ingredients. Stir well to combine.

Microwave on high for 60-75 seconds (using a 1100 watt microwave). 60 seconds results in a molten centre. 75 seconds will result in a more uniformly cooked brownie.

Serve topped with vanilla ice-cream. Take care, as brownie will be hot and will continue to cook while standing.