2 small onions, or one large one
2 cloves garlic (or more if you like)
1 tin diced tomatoes
1 x 500g jar of pasta sauce (garlic & herbs, or red wine & mushrooms)
2 rashers of smoked bacon with the fat trimmed off.
Optional: Mushrooms, herbs. Basil is a good one to throw in, or add whatever you reckon is a fair thing even if it's that red stuff in the jar at the back of the cupboard that no one knows what to use in, or even who bought it..
Dice the onions and bacon, and slice the garlic really finely. Lightly brown the meat in a pan with about 2 teaspoons of oil (olive, canola or sunflower) to stop it from sticking. Then dump in everything, and use the tomato tin to add that much water. It will look disgustingly watered down. Don't panic.
Put a lid on the pan and let it simmer for more than 60 minutes.
Stir it occasionally. When it has reduced from an ugly watery mess into a nice thick sauce, bung it onto some spaghetti.
Consume with beer.