In a microwave-safe mug add butter. Microwave it for 30 seconds.
Take the mug out of the microwave, and add grated cheese. Mix well.
After that, add milk, eggs, black pepper, salt and spring onions.
Using a fork, give everything a good whisk.
Place the mug back in the microwave, and microwave it for 1 minute.
Take it out and give it a stir. Again microwave it for 1 minute. You will notice that the eggs will start firming up in patches.
Note: Always cook in 30 seconds or 1-minute intervals. Otherwise, the egg might overflow.
Then take the mug out and add chopped sausage. Stir with a fork until well mixed.
Microwave for 1 minute. Take it out. Stir. By this time the omelette will be almost cooked.
Microwave for 1 more minute. Then take it out.
Note: If the eggs are still not cooked. Then continue microwaving it for 1-minute intervals until the egg sets.
Garnish with spring onions.