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.

Preheat oven to 400°F. Lightly oil 2 baking sheets.

Slice eggplants in half, place skin side up on a baking sheet, and pierce skin a few times.

Cut red bell peppers in half, seed them, place skin side up on second baking sheet. If desired, add optional hot red pepper. Roast together in oven until skin begins to char, about 20 minutes for peppers and up to 30 minutes for eggplant.

Remove bell peppers from the oven and place them in a covered bowl to steam skins loose. Let sit for 10 minutes. Use a sharp knife to peel skins off; discard skins. Place bell peppers in the bowl of a food processor fitted with a sharp blade.

Remove eggplant from the oven and let cool to the touch. Scoop eggplant flesh out, discarding seeds and skins. Place eggplant in the food processor with peppers, garlic cloves, salt as well as hot peppers if using. Pulse food processor on chop or puree on low, leaving the spread chunky or creating a smooth puree.

Scoop spread into a saucepan set over medium heat, add vinegar. Bring Ajvar to a boil, stirring constantly to eliminate splattering.

Ladle hot Ajvar into a hot jar leaving ½ inch headspace. Remove any air bubbles. Wipe jar rim. Center lid on jar and apply band, adjust to fingertip tight. Place jar on the rack in boiling-water canner with simmering water (180°F). Repeat until all jars are filled.

Water must cover jars by 1 inch. Adjust heat to medium-high, cover canner, and bring water to a rolling boil. Process half-pint jars 15 minutes, adjusting for altitude. Turn off heat and remove cover. Let jars cool 5 minutes. Remove jars from canner; do not retighten bands if loose. Cool 12-24 hours. Check lids for seal, they should not flex when center is pressed.