Place the butter in a large mug or medium microwaveable bowl. Microwave on high for 15-30 seconds, until melted. Add the milk and oil, and stir with a fork.
Add the chocolate mix and flour to the mug, and blend thoroughly with a fork until completely combined,
Cover with a paper towel and microwave on high for 60 seconds. Check for doneness and cook for 10 seconds at a time, until the brownie has puffed up and is no longer wobbly.
