
Several recipes on my blog use caramelised onions – they lift many savoury dishes. The Davinator who is sensitive to alliums (the onion and garlic family) can enjoy these onions as the aromatics have been cooked off. I make them overnight in the slow cooker. Quick to prep, minimises the crying and means you don’t have to watch them like a hawk to prevent scorching.
I’m working on a big post – my recipe for Epic Pie, adapted from a recipe by Fallow for Michelin quality Beef & Ale Pie. Caramelised onions are one of the (many) elements, hence this recipe.
I’ve included some tips for best outcomes in the recipe. Two overall recommendations: go big with the recipe you will not regret it. Second, learn to use a mandoline. Video evidence in the clip below but I can chop and slice an onion into the slow cooker in less than 60 seconds. It saves time and tears. It can be hard on the fingers in the beginning but it’s a skill worth mastering. That’s an Oxo Good Grips mandoline set to medium slice width.
Recipe
Ingredients
- 5 pounds (about 6–8 large) yellow or white onions (yellow onions work best for classic flavour; avoid sweet varieties like Vidalia if you want deeper caramelisation)
- 6 tablespoons butter (melted) or olive oil (or a mix of both for richness) — roughly 1 tablespoon fat per 2 onions
- 1 teaspoon salt (more or less to taste)
- Optional add-ins for extra flavour: 1–2 teaspoons brown sugar, 1–2 teaspoons balsamic vinegar, a few minced garlic cloves, or a pinch of black pepper
Instructions
- Peel the onions, cut in half and slice thinly (about ⅛–¼ inch thick) into half-moons. Use your food processor with the slicing disk or a mandoline.
- Add the sliced onions to your slow cooker, (fill it about halfway to three-quarters full for best results; too little and they may dry out or burn uneven). You’ll see in the video above I slice straight in the with mandoline.
- Drizzle the melted butter or olive oil and sprinkle the salt over the onions. Toss everything well with tongs or your hands until evenly coated. (Optional: stir in brown sugar or garlic here.)
- Cover and cook on LOW for 8–12 hours (most recipes land around 10 hours). Stir once or twice if you’re home, but it’s fine to leave them unattended. Some people prefer HIGH for 6–8 hours, but low gives more even, deeper flavour.
- Check at the end: The onions should be soft, greatly reduced in volume, and a rich golden-brown colour. If there’s excess liquid (common, as onions release a lot of water), prop the lid ajar for the last 1–3 hours to help it evaporate and thicken them into a jammy consistency. Taste and adjust seasoning — stir in balsamic or more salt if needed.
For best results
Know your slow cooker — Models vary in heat. Start checking around 8 hours. If the edges start browning too fast or sticking, give a stir.
For deeper caramelisation after slow cooking: Some people strain off the liquid, then finish the onions in a skillet or on the sauté function (if your slow cooker has one) for 8–10 minutes until glossy and darker.
If I’m making gravy or sauce for savoury pie, I strain off the liquid and add it to the gravy. It’s a little flavour bomb.


How to Use Caramelised Onions
- On burgers, sandwiches, or pizza
- For your savoury pies, focaccia
- In French onion soup, quiches, omelettes, or pasta
- Mixed into dips, mashed potatoes, or gravy
- As a side for steaks, roasts, or sausages
Storage
- Refrigerate in an airtight container for up to 1–2 weeks.
- Freeze in small portions (e.g., ice cube trays or silicone molds for ~2-tablespoon cubes) for up to 3 months. Thaw as needed — perfect for meal prep.
This is a forgiving recipe — experiment with the exact time and fat amount based on your slow cooker. The result is deeply sweet and savoury onions that elevate almost any savoury dish.
Thanks for reading the blog and trying the recipes. Always happy to answer questions in the comments.























