- Heat the olive oil and butter in a large pot.
- Stir in the chopped onions and garlic and sweat them over medium heat with the lid on.
- When the onions are tender, add the chopped canned tomatoes. (A hand blender works well for chopping.)
- Add sugar and salt and pepper to taste.
- Simmer covered for 1/2 hour. If you will be using it in a recipe that calls for further cooking, you can reduce simmering time to 15 minutes.
John Bishop writes, "This sauce can be made ahead and kept refrigerated for 5 days. I make it every week because it's so handy to have around...The secret is to keep the lid on while it's simmering. It results in a bright red, intensely flavoured sauce."