Start by caramelizing and dicing onions. You can caramelize on a cooktop or in your slow cooker.* I prefer to use my slow cooker and let it cook on its own overnight.
Add remaining ingredients to slow cooker and cook on low with the lid off for 2-3 hours until onions and liquid become thick.
Use an immersion blender to fully blend all ingredients
Allow to cool and enjoy
Optional Add-ins and Variations
Butter: For a richer onion jam, replace some olive oil with butter.
Rosemary: Add a single sprig (around 3-4 inches long) to the saucepan. Remove it before jarring the balsamic onion jam.
Oregano: A pinch of dried oregano would pair well.
Lemon: You can add lemon juice and zest to brighten the flavor.
Clove: Add a pinch of ground clove for depth.
Worcestershire sauce: A splash will add further depth.
Allspice leaves: You could use this instead of a bay leaf.
Ginger: Use finely grated ginger. I recommend ¼ tsp to begin and increase if you prefer a more robust flavor.
Garlic: I haven’t tried this, but I imagine adding a small amount of roasted garlic to the onion jam recipe would taste delicious.
Alcohol: Add a splash of port or bourbon towards the end.
Spice: Add a pinch of red pepper flakes OR some finely chopped chilies.
Mustard: A small amount of Dijon mustard helps to add depth and a slight heat.