How to Make It
In a medium enameled cast-iron casserole, cook the bacon over moderate heat, stirring occasionally, until crisp, about 11 minutes. Using a slotted spoon, transfer the bacon to a medium bowl. Pour off all but 2 tablespoons of the fat.
Add the onion, garlic and jalapeño to the casserole and season with generous pinches of salt and pepper. Cook over moderate heat, stirring occasionally, until the onion is very soft, about 12 minutes. Stir in the brown sugar and cook until the onion begins to caramelize, about 8 minutes. Pour in the vinegar and simmer until reduced by half, 2 to 3 minutes. Add the reserved bacon, tomato and tomato paste, cover partially and simmer over low heat, stirring occasionally, until a thick jam forms, about 45 minutes. Season with salt and pepper. Scrape the bacon jam into a jar and let cool completely before sealing with a lid.