The onions take their time – softening, collapsing, turning golden, then amber, then the color of old brass. The potatoes follow, breaking down just enough to make the broth velvety without feeling heavy. This caramelized onion potato soup is comforting but luxurious in the way only a home cooked meal can be.
If you love French onion soup but want something simpler and quicker, this is your new go-to soup. Made from humble ingredients, yet hearty and rich, this vegetarian dish – well, technically it does call for beef broth for added depth, but you can absolutely use vegetable broth instead – is budget-friendly and easily adaptable.
Topped with roasted mushrooms – another entirely optional and easily customizable addition – it adds layers of texture and deep, earthy richness, giving you different bites throughout and keeping each spoonful interesting and satisfying.
Why You’ll Love This Recipe
- Deep, umami flavor from slowly caramelized onions
- Naturally creamy texture
- Budget-friendly pantry ingredients
- Perfect make-ahead soup
- Can be made vegetarian and it’s easily adaptable
How to Make Caramelized Onion Potato Soup
Step 1: Caramelize the Onions and Fennel
In a large heavy-bottomed pot over medium heat, melt the butter. Add the sliced onions, fennel, and a generous pinch of salt.
Cook slowly for 30–40 minutes, stirring frequently and splashing in a little water as needed, until the onions and fennel turn a deep golden brown. Keep an eye on the heat and lower it if they begin to darken too quickly. When bits start to stick to the bottom of the pot, deglaze with a splash of water, broth, or white wine to loosen them and build flavor. Finish with the balsamic.
This step builds the entire flavor of your caramelized onion potato soup.
Step 2: Add Garlic and Potatoes
Stir in the garlic and cook for about 30 seconds until fragrant.
Add the diced potatoes, thyme, bay leaf, and broth. Bring to a gentle boil, then reduce to a simmer. Cook until potatoes are fork tender, about 20 minutes.
Step 3: Roast the Mushrooms
Toss the mushrooms with olive oil, salt, and za’atar until evenly coated. Spread them out in a single layer and roast at 400°F for 15-20 minutes, until browned at the edges and crisp.
Step 4: Blend Until Creamy
Remove the bay leaf.
Use an immersion blender to partially blend the soup, leaving some texture. For a smoother soup, blend completely.
You can stir in the cream at the end or drizzle it over each bowl before serving, which is how I prefer to do it. Taste and adjust the seasoning as needed.
What Are the Best Potatoes for Soup?
Yukon Gold potatoes are ideal for a creamy onion potato soup because they naturally thicken the broth without becoming gluey. Russets work too but will create a softer, thicker texture.
How to Properly Caramelize Onions for Soup
The key to deeply flavorful caramelized onion potato soup is patience:
- Medium to medium-low heat
- Stir every few minutes
- Allow natural sugars to develop
- Expect at least 30 minutes
Rushing this step results in sautéed onions, not caramelized ones.
Variations
French Onion Potato Soup: For a French onion twist, top with toasted baguette slices and melted Gruyère under the broiler.
Creamier Version: Add about ¼ cup heavy cream at the end.
Dairy-Free Option: Use only olive oil instead of butter and skip the creamy entirely or use coconut milk.
Add Protein: Crisp pancetta, bacon or shredded rotisserie chicken would work well here.
Storage & Make-Ahead Tips
- Refrigerate up to 4 days
- Freezes well for 2 months
- Reheat on the stove, adding more of broth if needed
What to Serve with Caramelized Onion Potato Soup
- Crusty sourdough bread
- Sharp cheddar grilled cheese
- Simple arugula salad with lemon vinaigrette
- Roasted chicken
Frequently Asked Questions
Can I make caramelized onion potato soup ahead of time?
Yes. In fact, it might even taste better the next day once the flavors settle.
Why is my onion soup bitter?
The onions likely cooked at too high a temperature. Caramelization requires slow, steady heat.
Can I freeze potato soup?
Absolutely, although texture may slightly change, but nothing too drastic.
You Might Also Like…
Spiced Squash & Lentil Soup with Caramelized Onion and Fennel: Sweet roasted squash and tender lentils meet caramelized onions and fennel in this cozy, spiced soup.
Sausage and White Bean Soup: Hearty sausage, squash, and white beans in a creamy, comforting broth.
Caramelized Onion and Pear Tart: Golden onions and tender pears baked into a flaky, sweet-savory tart.
Roasted Butternut Squash and Tomato Soup: Roasted squash and tomatoes blended into a silky, flavorful, and simple soup.
Caramelized Onion Potato Soup
Ingredients
- 1 tbsp butter
- 1 tbsp olive oil
- 2 medium onions, thinly sliced
- 1 tbsp medium fennel bulb, thinly sliced
- ½ balsamic vinegar
- 3 3 cloves garlic, minced
- 4 medium yellow potatoes, cut into chunks
- 3 cups beef broth
- 1 bay leaf
- 1 Small bunch thyme sprigs
- 200 g shiitake mushrooms
- 1 tbsp za'atar
- Heavy cream, for topping
- Parmesan cheese, for topping
- Fresh dill, for garnishing
Instructions
- Preheat the oven to 400°F.
- In a large pot set over medium heat, melt the butter with the olive oil. Add the sliced onions and fennel along with a pinch of salt, and cook slowly, stirring often, until soft and deeply golden, about 30-40 minutes. If they begin to darken too quickly, lower the heat and add a small splash of water to loosen any bits from the bottom.
- Stir in the balsamic vinegar and let it cook off for a minute.
- Add the minced garlic and cook until fragrant, about 30 seconds. Stir in the potatoes, then pour in the beef broth.
- Add the bay leaf and thyme sprigs, bring to a boil, then reduce to a gentle simmer. Cook until the potatoes are very tender, about 15-20 minutes.
- Meanwhile, toss the shiitake mushrooms with olive oil, salt, and the za’atar until evenly coated. Spread them out in a single layer on a baking sheet and roast at 400°F for 15-20 minutes, or until browned and crisp at the edges.
- Remove the bay leaf and thyme stems from the soup. Using an immersion blender, blend just a portion of the soup, leaving half of it textured (or lightly mash some of the potatoes to thicken the broth). Taste and adjust the seasoning as needed.
- Ladle into bowls and finish with a drizzle of heavy cream, grated Parmesan, the roasted mushrooms, and fresh dill. Serve.
