There’s nothing quite like slow cooker caramelized onions, and the way they go from crisp and sharp to soft, jammy, and impossibly rich. For years, I stood over a skillet, stirring endlessly, convinced that was the only way. Then, one day, I threw a pile of onions into my slow cooker, walked away, and came back to absolute magic. No babysitting, no constant stirring—just perfectly golden, sweet-savory onions that taste like they’ve been cooking for days. Now, I always keep a batch in my fridge because, let’s be honest, everything tastes better with caramelized onions. Burgers, soups, sandwiches, or straight from the spoon? No judgment.
This post contains helpful tips and tricks! If you’re in a rush, please use the “Jump to Recipe” above!
💭 Sweet, savory, and perfectly jammy every time!
Let’s be real—standing over a stovetop stirring onions for an hour isn’t exactly my idea of fun. That’s why I love this slow cooker method! The onions cook down into pure golden magic while I go about my day, leaving my kitchen smelling incredible. Whether you’re using them for soups, sandwiches, or just as an excuse to eat something caramelized by the spoonful, these onions will be your new secret weapon in the kitchen.
Make these as part of my delicious French onion soup (or the slow cooker version made entirely in the slow cooker).
Shruthi’s Top Tip
Slice the onions evenly—thin, uniform slices ensure they cook at the same rate and caramelize evenly.
- Don’t crowd the slow cooker too much; the onions need room to soften and develop their flavor properly.
- No need to add water, onions naturally release a lot of liquid while cooking, so they’ll create their own liquid in the slow cooker.
- Keep the lid slightly open—this lets excess moisture escape so the onions caramelize instead of steaming. If the onions release too much liquid, crack the lid open wider or turn the heat to high for the last hour to evaporate moisture.
- Stir every couple of hours if possible; it helps distribute heat and prevents onions at the edges from overcooking.
Variations & Substitutions
- Use sweet onions or yellow onions for the best balance of flavor, though red onions will give a deeper, slightly tangy twist.
- A touch of sugar speeds up caramelization, but feel free to skip it if you prefer a more natural sweetness. I like to use brown sugar for a deeper flavor.
- If you love extra buttery onions, stir in an additional tablespoon of butter in the last hour of cooking.
- To make it vegan, use olive oil instead of butter.
📖 How to make slow cooker caramelized onions
Step 1:
Set your slow cooker to high. Add melted butter (or olive oil), sliced onions, and sugar (if using). Stir to coat the onions evenly.
Step 2:
Prop the lid open slightly to allow steam to escape and cook for 6-8 hours on low heat, stirring occasionally, until onions are golden brown and soft.
Step 3:
Add balsamic vinegar and sherry to deglaze the slow cooker. Stir well to pick up any browned bits.
🍴 How to serve crockpot caramelized onions
There are so many ways to use caramelized onions! Slather them on toast or crostini, melt them into a grilled cheese, top your pizza with their sweet-savory flavor, or go full bistro with French onion soup. The sky’s the limit!
🍴Storage and reheating suggestions
Store leftovers in an airtight container or jar in the refrigerator for up to a week.
Make a big batch of these caramelized onions, divide them into small portions into a freezer bag, then freeze for up to 3 months. They defrost beautifully and are perfect for soups, sandwiches, or as a pizza topping.
🍴 More slow cooker recipes
If you like this recipe, check out my other slow cooker recipes:
High Protein Vegetarian Dinners
Marinated Tofu (+6 Marinades)
Spicy Soba Noodles
Silken Tofu Chocolate Mousse
If you tried this recipe, don’t forget to comment and rate! ⭐⭐⭐⭐⭐
Slow Cooker Caramelized Onions
Equipment
Ingredients
- 4 large yellow onions, thinly sliced
- 2 tbsp butter, or olive oil for a vegan option
- 1 tbsp sugar
- 1 tbsp balsamic vinegar, optional
Instructions
- Set your slow cooker to high. Add melted butter (or olive oil), sliced onions, and sugar (if using). Stir to coat the onions evenly.
- Prop the lid open slightly to allow steam to escape and cook for 6-8 hours on low, stirring occasionally, until onions are golden brown and soft.
- Add balsamic vinegar and sherry to deglaze the slow cooker. Stir well to pick up any browned bits.
Notes
- Keeping the lid slightly open helps excess moisture escape, allowing the onions to caramelize rather than steam. If your slow cooker doesn’t allow this, you can prop it open with a wooden spoon.
- Stirring every few hours ensures even cooking and prevents burning at the edges.
- The sugar helps accelerate caramelization, but you can omit it if you prefer a more natural sweetness.
- Butter adds a rich depth of flavor, but olive oil is a great vegan alternative.
- Store caramelized onions in an airtight container in the fridge for up to one week, or freeze them in portions for up to three months for easy use in recipes.
Curious why you say set your slow cooker to high, then it says cook for 6-8 hrs on low?
Hi, you can cook on high for 3-4 hours or slow for 6-8 hours!