Tomato Sauce

Ingredients
400 gram can peeled plum tomatoes, no salt or herbs added
75g unsalted butter
1 small white onion, peeled and cut in half
salt
To serve
Shaved Parmesan cheese
Freshly ground black pepper

Method
Put a saucepan over medium-high heat.
Add the tomatoes, butter, onion halves, and a pinch of salt.
Bring to a simmer then lower the heat.
Crush the tomatoes lightly with the back of a spoon as they cook, and stir occasionally.
Simmer very gently for 45 minutes, or until droplets of fat appear on the surface of the tomatoes. Remove and discard the onion.
Serve over hot pasta with Parmesan and black pepper, if desired.