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Just three ingredients and a Slow Cooker — that’s all it takes to make this deeply comforting onion and potato soup. The onions go silky and golden, the potatoes turn tender and creamy, and the broth gets rich and slightly thickened all on its own. It’s humble food that tastes like you did a lot more work than you did.
Why You’ll Love It
Only 3 ingredients — potatoes, onions, and broth; nothing fancy required
Completely hands-off — the Slow Cooker does all the work while you go about your day
Naturally thick and creamy — no cream, no blender; the potatoes break down and do it themselves
Budget-friendly — one of the most affordable meals you can make, and it feeds a crowd
Deep, rich flavor — low and slow heat turns simple onions into something genuinely sweet and savory
Ingredient Notes
Yellow onions. Please use yellow onions. I’ve tried this with sweet onions and they go almost jammy — which isn’t bad, exactly, but it’s different. More like French onion soup’s softer cousin. White onions get a little sharp. Yellow onions hit the right note: they mellow out and get genuinely sweet without tipping over into dessert territory.
For potatoes, I use russets because they break down at the edges and naturally thicken the broth, which is exactly what you want. Yukon Golds work too — a little creamier — but the broth doesn’t get quite as thick.
Beef broth. I buy the cartons, whatever’s on sale. I’ve used Better Than Bouillon dissolved in water and honestly I think it’s just as good. If you want to keep it meatless, vegetable broth works fine. Chicken broth makes a lighter soup that’s also very good — maybe a little more delicate, less of that deep savory warmth, but still absolutely worth making.
Ingredients
3 large yellow onions, thinly sliced — root to tip, long slices, don’t rush this part
4 large russet potatoes, peeled and cut into chunks (I go about an inch and a half, maybe two inches — I eyeball it, honestly)
6 cups beef broth, or vegetable broth if you prefer
Instructions
Peel the onions and slice them thin. I do this the long way — root to tip — because I think they soften more evenly that way. My eyes water every single time and I’ve tried every trick: the frozen onion thing, the candle thing, cutting near the stove vent. Nothing works. I just cry into my cutting board for a few minutes and carry on.
Peel the potatoes and cut them into honest chunks. Not tiny — you want them to hold up through the long cook. I’d say an inch to an inch and a half, maybe bigger. They’ll shrink a little.
Go ahead and put the onions in the Slow Cooker first. Spread them out over the bottom. Then pile the potatoes on top. Then pour in all that broth. Give it a very gentle press down with the back of a spoon so everything is mostly submerged — you don’t need to be aggressive about it. Don’t stir. Just settle it.
Put the lid on and walk away.
Low for eight to ten hours. High for four to five if you’re in a hurry, though I think the longer cook makes better soup. The couple of times I’ve done it on high I felt like something was missing — the onions hadn’t fully surrendered yet, I guess.
When it’s done — and you’ll know because your whole house will smell exactly like something made in a kitchen with checkered linoleum and a window over the sink — give it a gentle stir from the bottom up. Some of the potatoes will break apart. That’s what you want. That’s what thickens it.
If you want it thicker, use a potato masher right in the pot. Smash maybe a third of the potatoes and stir it all together. It goes from brothy to almost silky. Both versions are right.
Taste it. Add pepper if you want. Salt if it needs it, but the broth usually handles that.
Ladle it into bowls — make sure you get onions and potato in every bowl, don’t just skim the top — and serve it with bread. Thick bread. Buttered bread if you have it.
Variations
Sometimes a little garlic — just a clove or two thrown in at the beginning — works nicely here, though I keep not doing it myself. There’s something about the purity of three ingredients that I’m reluctant to mess with. I’ve earned my stubbornness at this point.
If you want it creamier, you could stir in a small splash of heavy cream at the end. I’ve done this exactly once. It was good. But it changes the whole personality of the soup — it goes from honest to indulgent, which is fine but not what I usually want from this particular recipe.
Storage
It keeps well in the fridge for three or four days. I find the flavor actually deepens overnight — day two might be better than day one, which I always find slightly annoying, like the soup is showing off. Reheat it gently on the stove and add a splash of broth or water if it’s thickened up too much in the fridge, which it will.
I have left this out on the counter too long more than once. We don’t need to discuss that.
This is the kind of soup that asks very little and delivers a lot. Serve it hot, use a good bowl if you have one, and don’t skip the bread. That’s really about all.
Slow Cooker 3-Ingredient Onion and Potato Soup
Ingredients
- 3 yellow onions thinly sliced
- 4 russet potatoes peeled and cut into chunks
- 6 cups beef broth or vegetable broth
Instructions
- Place sliced onions evenly in the bottom of the slow cooker.
- Add chopped potatoes on top of the onions.
- Pour broth over everything and gently press down so ingredients are mostly submerged.
- Cover and cook on LOW for 8–10 hours or HIGH for 4–5 hours.
- Stir gently, allowing some potatoes to break apart and thicken the soup.
- Optional: mash a portion of the potatoes for a thicker, creamier texture.
- Season with salt and pepper if needed, then serve warm.
