Sauté the onions, garlic, salt and black pepper in the oil. When the onions are very soft and starting to caramelize (kinda sticking to the bottom of the pot), add the tomatoes and bring to a simmer. Let simmer for 20 minutes. Be sure to stir the sauce frequently. Onions and tomatoes have a lot of natural sugars that like to “catch” on the bottom of a pot and subsequently burn.
Add zucchini, red pepper, fennel, fennel seed and chili flakes, then simmer another 10 minutes.
Add oregano, basil, parsley, capers, olives and simmer gently for 5 minutes.
Jar immediately, pasteurize for 10 to 15 minutes then allow to stand until cool. Lids will “pop” once sealed (see page 31 for method).
Store on shelf or in the fridge for up to 6 months. Adjust seasoning when reheating.