Preheat oven to 425°.
Set peppers on a baking sheet and sprinkle with 2 tablespoons olive oil.
Roast in the oven 15-20 minutes or until soft and skins begin to blister.
Heat a large pot to medium heat and add remaining ingredients. Bring to a boil then reduce heat to low and simmer about 20 minutes, or until onion and garlic soften.
Add roasted peppers and simmer about 5 minutes.
Transfer mixture to a food processor and puree until smooth. Alternatively, use an immersion blender and puree directly in the pot.
Simmer another 5-10 minutes.
Serve, or strain into sterilized bottles until ready to use.
