Heat a large skillet over medium heat, then add cut bacon, spreading into a single layer to crisp up. Cook, stirring occasionally, until bacon is crispy, about 8-10 minutes. The fat from the bacon will render out, so no need to add any oil or nonstick spray!
While bacon is cooking, prepare a large plate with paper towels. Once bacon is finished cooking, remove with a slotted spoon onto paper towel plate. Drain bacon fat from pan, leaving about 2 tbsp. worth (don’t drain down the sink!).
Add diced onions and salt to the skillet, stirring around to pick up any leftover bacon bits. Cook, stirring occasionally, until onions are jammy and slightly caramelized, about 10 minutes.
Add in bacon, balsamic vinegar, coffee, cinnamon, and brown sugar, and 1/4 cup water, stirring until well combined. Cook in a single layer until liquid evaporates and bacon-onion mixture becomes thicker, about 10-12 minutes.
Allow bacon-onion jam to cool before transferring to jar or airtight container. Keep in the fridge for up to 5 days.
