Roasting tomatoes and garlic brings out a sweet smokiness, adding a deep, rich flavor dynamic to your sauce.
Roast tomatoes, in batches, on a grill or under a broiler until skins begin to wrinkle and blacken slightly, turning to roast on all sides. Repeat with remaining tomatoes. Place finished tomatoes in a large bowl.
Cover bowl of tomatoes tightly with plastic wrap. Let tomatoes steam and cool until they are easy to handle.
Remove peel and core tomatoes. Slice each one in half and remove seeds; dice into 1-inch chunks. Place diced tomatoes, and any collected juices, into a large saucepan.
Slice top portion off the heads of garlic, revealing the cloves below, drizzle 1 teaspoon olive oil over cloves in each head.
Wrap garlic tightly in aluminum foil and place top side down on the grill with tomatoes; grill until soft, about 30 minutes. Or, roast in a 350° oven for 60 minutes.
Prepare boiling water canner. Heat jars in simmering water until ready to use, do not boil. Wash lids in warm soapy water and set aside with bands.
Remove roasted garlic by squeezing the softened heads of garlic allowing the cloves to pop out. Combine garlic, onions, herbs, salt, and pepper with tomatoes. Cook over medium heat until heated through, stirring occasionally.
Add ½ teaspoon citric acid or 2 tablespoons lemon juice to a hot jar; ladle hot sauce into a hot jar
leaving a ½ inch headspace.
Remove air bubbles.
Wipe jar rim.
Center lid on jar and apply band, adjust to fingertip tight. Place jar in boiling water canner. Repeat until all jars are filled.
Process jars 40 minutes, adjusting for altitude. Turn off heat, remove lid, let jars stand 5 minutes. Remove jars and cool 12-24 hours. Check lids for seal, they should not flex when center is pressed.