Heat oven to 480F, or if you are using a wood stove, heat it up high.
Thoroughly wash, then pat dry whole eggplants and horn peppers. If you are using a wood stove, place foil on top of it and roast the peppers first. If using a regular stove, use both racks. (If you only have one rack then use the rack plus the bottom of your oven.) Cover a baking sheet with foil (or the rack itself if you don't have a baking sheet), and line it with as many peppers as you can, leaving a bit of space between them, then place inside. Repeat for the second rack, or bottom of the oven. You'll have to do this in two to three batches for the peppers.
Roast peppers for about 25-30 minutes (check once or twice), then turn them over if they’re done on the bottom end. They should have little black patches here and there, and the skin will be coming up. They’ll also be soft, and will exert some of their fluid. For the next 20-25 minutes frequently check the peppers, and turn them to the side if necessary to make sure they’re roasted on all sides. At about 50-55 minutes of roasting, they should be completely roasted. Don’t be overly concerned with time, instead, watch that peppers are completely roasted, but not burned. It’s possible that one rack will be done, while the other still needs a little bit of time. So the timing here is only an indication. All depends on your oven and peppers.
Take the roasted peppers out. Place them in a couple of different bowls, and cover bowls with plastic bags, making sure to seal really well. Leave to cool overnight.
Repeat the previous two steps for all peppers.
At this point roast eggplants the same way as peppers. They may need a little bit less time, but it’ll depend on your oven. When done the eggplants will also “raise” their skin, and will also have a few brown black patches. They’ll be soft and moist. After you’re done, place them in bowls and cover with plastic bags (optionally you can leave them in a bowl overnight uncovered). Leave to cool overnight. (This is a good stopping point. You are welcome to peel the same day, you can even cook ajvar the same day. But it’ll tire you. Also it’s good to give the veggies some time to cool off. It’ll be easier to peel them, and you’ll protect your hands from burns.)
The following day, start peeling eggplants and peppers. This part is messy, so protect your working area, whether it’s the floor or the table or the counter. Prepare a large bowl with water, and one to two large bowls in which you’ll place peeled peppers and eggplants. Also prepare a few plastic bags you’ll use for trash. (If ever, this is the time to get your family involved. Peeling is a long and tedious process.) Put on your gloves. Start peeling peppers by removing the stem and discarding it. Then flatten out the pepper so you can see its insides, and dip in water to remove the seeds. The next step is to peel off all of the skin, and black dots that formed while roasting. This is a tricky part as you may lose some of the pepper meat, and even some of the peppers, as they might be of a bad quality and are too thin to peel. You can peel them with your fingers or a knife. You’ll find you have a preferred way of doing it. Once a pepper is peeled, transfer it to a dry bowl and repeat this process until all your peppers are peeled.
Move on to peeling eggplants by cutting off eggplant stem and discarding it. Then use a knife to take off its skin and black dots that formed while in the oven, while keeping as much meat and seeds in tact as possible. You will be using seeds from the eggplant, so no need to remove them. After peeling, transfer to a dry bowl that’s separate from peppers.
The next step is to either cut or grind down eggplants and peppers. Keep them separate. Start with the eggplant first. If you choose to cut them down, ajvar will be tastier and chunkier. But will take a long time. If you opt for this, cut the vegetables (separately, and eggplant first) into stripes first, and then dice into smallest possible pieces, while keeping the juices. If you use the grinder, grind each vegetable down into a separate pan, again keeping the juices.
Take a large pot that will fit in all ingredients and still have a few empty inches on top. Fill it with oil the thickness of one finger. Warm up the oil until really hot on high, and add eggplant. Stir eggplant in really well, and simmer for 15-20 minutes. Stir frequently.
Bring down the temperature to low and add grinded peppers in. Stir well. Ajvar will be cooking for the next four and a half to five hours (please see my note about stoves regarding the time). The ingredients will essentially be boiling most of the time, and the air bubbles will be coming out. It’s imperative to continue stirring ajvar throughout the entire cooking time, that's every few minutes, to prevent burning. You will also be adding about 3-4 cups of oil to the pan throughout the cooking process, a little at a time every fifteen minutes or so. Stirring is a tedious process, but if you skip it, your entire effort will be wasted. Basically, as you are stirring ajvar, you are making sure it’s not burning, and you’re adding some oil at regular intervals while stirring.
After about four hours of cooking, add in sugar and continue stirring.
At the very end of cooking, after about four and a half to five hours, add in salt. Meanwhile, heat oven to 250F. Wash several jars in hot, soapy water and rinse well. Pat dry. Place on a baking sheet and put in the oven. Warm them up for fifteen minutes. This will sterilize them.
Once the jars are hot, and the ajvar is turned off (it’s still extremely hot so be careful) you’ll be transferring hot ajvar to hot jars. If you have another pair of gloves this is a good time to wear them. Use thick kitchen mittens to pick up jars to protect your hands and fingers. Be very careful while you transfer ajvar into jars. Do jars one by one, and fill each up to the top, leaving the part where the ridges empty (so fill up almost to the top, leaving the top portion empty).
After you’ve filled up a jar, take a spoon, and press ajvar all the way into the jar, making sure there are no air bubbles left in the jar. Air is what makes ajvar go bad, so do not skip this step. Do it meticulously and do it for every jar.
When all the jars have been filled up, place them on a baking sheet and return to the warm, but turned off oven, without lids. It’s best if they’re left overnight, or at least several hours. A crust will form on the top of ajvar in each jar. The crust is basically ajvar that’s hardened and darkened. This will be a thin but hard layer. At this point, take out the jars, pour a few tablespoons of oil on top of the crust in each jar, and screw lids on tightly.
Keep ajvar in a dark and cool place. There is no need to it in the fridge until you open the jar. However, as soon as you open each jar, when not eating ajvar, it will have to be in the fridge. As you open a jar of ajvar for the first time, first pour out the oil that was on top, stir the ajvar in jar, and then use.
Ajvar can last several months like this. Of course, it won’t last that long because it’s too delicious.