To grill the eggplants, make sure you poke holes with a knife, so they don't explode. Grill them until soft and charred. After the eggplants have cooled off, remove the peel, using a knife, if you've cooked them enough, the peel should come off easily.
Grill the peppers, or roast them in the oven until they are almost completely charred.
Let cool and remove all the peel and seeds from them and wash them well.
Place the eggplant in a colander and let it drain off any excess water. Do the same with the peppers. This may take about half hour or so.
The next step you can do in small batches, depends how big your food processor is, but place some eggplant into the food processor and pulse a few times until the eggplant is finely chopped but you don't want it to be look like a paste. Repeat the same with the peppers.
In a very large pot heat the oil and add the onions. Cook the onions until soft, make sure not to burn them. They should just start to change color.
Carefully add the eggplant and peppers and stir using a wooden spoon. Add tomato sauce. Add the salt, black pepper and bay leaves. This will require 3 hours of cooking over low to medium heat, stirring occasionally, I stirred every 10 minutes, just so that it doesn't stick to the bottom.
In the meantime, boil the jars in hot water first for about 10 minutes. After that, just before the spread is ready to be canned, you place the jars, lids off, in the oven at 180 F degrees for 10 minutes. Take them out and carefully fill the jars so that there is about an inch left from the top, place the lid onto the rim and, using one finger to hold the lid securely, twist on the screw band until it’s tight. Once this is done with all the jars, place them back in the oven and continue baking for another 15 minutes, after which you can turn off the oven, and let them cool in there.