1 onion
1 clove garlic
1 tbs tomato puree (paste)
1 tin tomatoes
A little extra water
Seasoning.
Microwave onion and garlic for about 3 minutes; transfer to saucepan with the tomato puree, stir, add tinned tomatoes and a little water, season, bring to the boil and simmer for about 15 minutes. If it's a bit liquid, boil harder to reduce - get it to the sort of consistency you would like.