Line a small baking sheet with parchment paper. Place the onions and garlic on the baking sheet, and drizzle with olive oil.
Roast at 375°F until the onions are tender and golden brown.
Transfer the roasted onions and garlic to a blender or food processor when done roasting, along with the drained roasted red peppers. Blend until smooth.
Peel tomatoes. Cut tomatoes in half horizontally and squeeze out the seeds. Cut tomato halves a second time to form quarters.
Put quartered tomatoes in low sided saucepan or skillet over medium-high heat.
Pour in the onion and garlic puree. Add salt, olive oil, tomato paste, basil, and bay leaves.
Bring to a boil, then lower the heat to a brisk simmer.
Continue simmering without a lid until the sauce is reduced by almost half, stirring occasionally, to produce about 2 cups of medium-thick sauce. This should take approximately 20 minutes.
Remove dried bay leaf. Taste and adjust salt.
Notes
For a smoother sauce, stir with an immersion blender.It will keep up to 5 days in the fridge or may be frozen.