Put a good glug of olive oil in a medium saucepan over a low heat. The actual recipe I use states 8-10tbsps but that seems ever such a lot. Peel a small onion and fry gently in the oil for 6-8 minutes, stirring occasionally. The onions should be translucent and golden in colour. Cooking them for this long gives the sauce its sweetness.
Roughly chop a punnet of ripe fresh tomatoes (approx 750g) and add to the pan. I tend to chop them on a plate rather than a board to stop the juices escaping. Peel three cloves of garlic and add them whole to the pan. Season well with freshly ground pepper. You could add salt too but I don't think it is needed. Break the tomatoes down a little with a wooden spoon.
Add either a 400g tin of tomatoes or a small carton of passata. Add 100ml of vegetable stock and turn the heat up until it begins to simmer. Cook for approx 30-45 minutes. I often transfer it to the slow cooker as it means I don't need to keep an eye on it.
At this point you could blitz the sauce with a hand blender, check the seasoning and serve as it is. I prefer to add a handful of fresh basil and a small tub of mascarpone cheese, warm through and then blitz it.
I feed two adults and four children most evenings. I find this recipe makes enough for two meals so I freeze half for another day. Another variation is to add a few teaspoons of dried red chilli flakes rather than the mascarpone for a spicy version more suited to adults.