250 gr small pasta, such as penne
800 gr peeled canned plum tomatoes (or chopped tomatoes). I always use a combination of canned tomatoes plus some fresh tomatoes that I cream in the food processor.
5 tbsp unsalted butter
1 large onion, peeled and halved
4 garlic cloves, peeled and smashed
1-2 pinches red pepper flakes
salt, red wine vinegar
100-150 gr parmesan cheese, grated
3 balls fresh mozzarella
fresh basil leaves
Place the tomatoes with their juices into a saucepan and add the butter, onion halves, garlic, red pepper flakes and salt.
Cook over medium heat stirring, for about 20-30 minutes (30-45 if you're making double the sauce).
Remove from the heat and discard the onion halves. Put the sauce in a food processor and blend until as smooth as it can be.
Return in to the saucepan and simmer over low-medium heat for 20-30 more minutes (30-45 if you have doubled the quantities) or until the sauce has thickened to a good consistency (you don't want it to be too loose). Taste and adjust the salt, or add a splash of vinegar.
Preheat the over to 200 C.
Before the sauce is ready, cook the pasta in salted water, drain it and toss it with half of the tomato sauce and a handful of parmesan.
Put a layer of pasta in a baking pan ( mine is a small one, as per the picture below. If you have doubled the quantities, use a larger one) followed by some of the remaining tomato sauce, a handful of parmesan, some chunks of mozzarella, and a couple of torn-up basil leaves. Then repeat these layers until all the ingredients are gone, ending with a layer of cheese on top.
Bake for about 15 minutes, or until warm and bubbling and golden on top.