This roasted garlic and sweet onion soup is pure comfort in a bowl!
It’s rich, velvety, and packed with deep caramelized flavor thanks to a full head of roasted garlic and sweet, slow-cooked onions.
Whether you’re craving something cozy on a rainy day or looking for a unique twist on classic onion soup, this creamy version brings out the best of both worlds.
Why You’ll Love This Recipe
Naturally sweet and savory thanks to caramelized onions and roasted garlic.
Creamy without needing heavy cream—milk and broth keep it light but luscious.
A vegetarian soup that feels indulgent but wholesome.
Perfect for meal prep and reheats like a dream!
Ingredient Highlights
Here’s what makes this roasted garlic and sweet onion soup irresistible:
Whole garlic head: Roasting brings out a sweet, nutty depth.
Sweet onions: Thinly sliced and slowly caramelized for maximum flavor.
Leeks: Adds a delicate, grassy onion flavor to balance the sweetness.
Dry white wine: Adds brightness and a touch of acidity.
Vegetable broth + milk: Makes it creamy yet light.
Dried thyme: Earthy and aromatic, the perfect pairing for garlic and onion.
Flour: Just a little, to help thicken the soup.
Fresh thyme and black pepper: Optional garnishes for a beautiful finish.
Pro Tips Before You Start
Slice your onions and leeks very thinly for faster caramelization.
Use a good quality vegetable broth for deeper flavor.
If using milk alternatives, choose unsweetened versions that won’t overpower the dish.
Roasting garlic ahead? You can store it in the fridge for up to 5 days.
How to Make Roasted Garlic and Sweet Onion Soup
Step 1: Roast the Garlic
Preheat your oven to 350°F. Trim the top off a whole garlic head, drizzle with olive oil, and wrap in foil.
Roast for 1 hour. Let it cool, then peel the cloves and set aside.
Step 2: Caramelize the Onions and Leeks
In a large pot, heat the remaining olive oil over medium heat.
Add sliced onions and leeks. Cook uncovered, stirring often, for 30 minutes.
Sprinkle in half the salt and the thyme.
Continue cooking another 30 minutes, scraping up browned bits and adding a splash of water if needed.
Step 3: Build the Base
Sprinkle in the flour and cook for 1 minute, stirring constantly.
Add the wine and broth. Bring to a boil, then reduce heat and simmer for 30 minutes to deepen the flavor.
Step 4: Blend Until Creamy
Add the roasted garlic cloves to a blender with the cooked onion mixture and remaining salt.
Blend until completely smooth (in batches if necessary).
Step 5: Simmer with Milk
Return the blended mixture to the pot.
Stir in the milk and simmer gently for about 8 minutes until heated through. Do not boil.
Step 6: Garnish and Serve
Ladle into bowls and garnish with fresh thyme and a few grinds of black pepper.
Serve hot with crusty bread or a side salad.
What to Serve It With
Crusty baguette or garlic bread
Grilled cheese sandwiches
A crisp green salad with vinaigrette
Roasted potatoes or vegetables
Variations & Substitutions
Add a splash of cream if you want a richer texture.
Make it vegan by using non-dairy milk like oat or almond.
Try different onions like Vidalia or red for variety.
Add heat with a pinch of chili flakes or cayenne.
Storage & Leftovers
Refrigerator: Store in an airtight container for up to 5 days.
Freezer: Freeze for up to 2 months. Thaw overnight and reheat gently on the stove.
Reheat: Warm over medium heat, stirring often. Add a splash of broth if needed.
FAQs
How do I prevent the onions from burning?
Keep the heat at medium and stir often.
Add small splashes of water if the onions begin to stick or brown too quickly.
Can I skip the wine?
Yes, just replace it with more broth or a little lemon juice for acidity.
Can I use yellow onions instead of sweet onions?
Absolutely! The soup will still be delicious, just slightly less sweet.
What’s the best milk to use?
Whole milk gives the creamiest texture, but 2% or non-dairy milk also works well.
Can I make this ahead of time?
Yes, this soup actually tastes even better the next day after the flavors meld!
Is this gluten-free?
Not as written, but you can use a gluten-free flour or cornstarch slurry to thicken.
Can I add cheese to this soup?
Yes! Stir in a handful of shredded Gruyère or Parmesan at the end for extra richness.
Final Thoughts
This roasted garlic and sweet onion soup is everything I love about comfort food—simple ingredients, big flavor, and that irresistible creamy texture.
It’s a soup that feels cozy, a little fancy, and just right for any season.
Roasted Garlic & Sweet Onion Soup
Ingredients
- 1 large whole garlic head
- 1 ½ tablespoons olive oil divided use
- 9 cups about 4 large thinly sliced sweet onions
- 2 ½ cups about 2 medium sliced leeks (light green and white parts only)
- 1 teaspoon salt divided use
- 1 teaspoon dried thyme
- 2 tablespoons all-purpose flour
- ⅓ cup dry white wine
- 4 cups vegetable broth
- 2 cups milk
- Fresh thyme leaves for garnish
- Freshly ground black pepper for garnish
Instructions
- Preheat oven to 350°F. Rub garlic head with ½ tbsp olive oil and wrap in foil.
- Bake 1 hour, cool, peel cloves, and set aside.
- Heat 1 tbsp olive oil in a large pot over medium heat. Add onions and leeks.
- Cook uncovered, stirring often, for 30 minutes.
- Add ½ tsp salt and thyme. Cook another 30 minutes.
- Stir in flour and cook 1 minute. Add wine and broth.
- See full steps with tips & photos → https://wimpysdiner.net/roasted-garlic-and-sweet-onion-soup/
Notes
- Flavor Boost: Use a splash of sherry instead of white wine for deeper complexity.
- Make-Ahead: Caramelize onions and roast garlic up to a day ahead; refrigerate and assemble before reheating gently.
- Dairy-Free Option: Swap milk for unsweetened almond or oat milk and use dairy-free butter.
