Slow Cooker Caramelised Onions
Slow cooker caramelised onions softened slowly, then finished hot for proper browning and a deep, savoury flavour.
Equipment
- Slow Cooker
- Wide Frying Pan
- Instant Pot optional
- Kitchen Machine optional
Ingredients
- 1.6 kg onions yellow or white, thinly sliced
- 30 g unsalted butter or 30 ml olive oil, or a mix
- 1.5 tsp fine salt
- 10 g brown sugar about 2 tsp (optional)
- 15 ml balsamic vinegar or cider vinegar optional, added at the end
Instructions
- Add the sliced onions to the slow cooker (or Instant Pot on slow cook mode). Add the butter (or oil), salt, and sugar if using, then toss well to coat.
- Cover and cook on LOW for 10 hours, until the onions are fully softened, collapsed, and very pale golden. Stir once or twice if convenient.
- If there is a lot of liquid, uncover and cook on HIGH for 30–60 minutes to reduce, or carefully pour off some of the liquid to speed up the finish.
- Finish over higher heat: switch the Instant Pot to sauté (high), or transfer the onions to a wide frying pan over medium–high heat.
- Cook for 10-15 minutes, stirring frequently, until darker, glossy, and thick enough to mound on a spoon. Reduce heat if they begin to catch.
- Taste, adjust seasoning if needed, then stir in the vinegar right at the end (if using). Cool before storing.
Notes
- Fat choice: Butter gives a rounder flavour; olive oil tastes cleaner; a 50/50 mix is a good middle ground.
- Herb variation: Add 2–3 sprigs thyme or 1 bay leaf during the slow cook, then remove before the final high-heat stage.
- Deeper, darker finish: Stir in 1–2 tsp balsamic vinegar at the end, or add 1 tsp soy sauce during the final 2–3 minutes for extra savoury depth.
- No sugar: It’s optional—onions will still caramelise with time. If you prefer a less sweet result, leave it out and rely on the vinegar at the end for balance.