Caramelized Onion Fennel and Mushroom Soup – Hearty, Savory, Satisfying
The trees, the mountains, the roads, the grass, the garden, the sidewalks—everything covered in white the other morning with six inches of new-fallen snow. Despite the freezing temperature outside, bowls of deeply satisfying 
Caramelized Onion Fennel and Mushroom Soup with Toasted Quinoa had us feeling warm and cozy inside. The Rich Mushroom Stock, deeply caramelized onions and fennel along with an abundance of fresh mushrooms create an umami-rich and savory gluten and dairy-free soup. A scoop of Toasted Quinoa adds heartiness to the soup making it a meal-in-a-bowl. Without the quinoa, serve the soup as a first course.
A weekend project or over a few days
Over this past week I’ve shared with you the recipes for preparing Rich Mushroom Stock and Toasted Quinoa. With today’s recipe for Caramelized Onion Fennel and Mushroom Soup (print recipe) you’re good to go. 
Making a pot of this hearty, satisfying soup makes a great Sunday or weekend project.
Or, spread the prep out over a few days. You could make and refrigerate the Rich Mushroom Stock up to 3 days in advance (or it can be made and frozen for up to 6 months). And, you can both slice the onions and fennel and caramelize them up to a few days in advance as well. With so much completed, you’ll make quick work of preparing the soup and the Toasted Quinoa.
Caramelized onions done right
For a number of years, I didn’t understand the fuss over caramelized onions. Then I came across an article in Lucky Peach Magazine by Chef David Chang on the correct way to caramelize onions. Oh my, what a difference technique and time made. These caramelized onions are fuss-worthy.
Recipes for caramelizing onions often haven’t told the whole story. Many food writers have written to cook them for 10-20 minutes until golden and you’re done. (I did the same following their lead, as I didn’t know any better.)
No way. True caramelized onions can’t be rushed. They require long, slow cooking to allow the natural sugars trapped inside the onion layers to caramelize without burning. Allow about an hour for tender, sweet and hauntingly savory, deeply caramelized onions.
Caramelized Onion Fennel and Mushroom Soup with Rich Mushroom Stock and Toasted Quinoa
Deeply flavorful and rich broth filled with caramelized onions and fennel and lots of sautéed mushrooms. As the quality and flavor of your stock holds the key to this flavorful vegetarian soup, do make your own Rich Mushroom Stock. For subtle variations in flavor, switch up the varieties of mushrooms. And, for a heartier bowl of soup, serve Caramelized Onion Fennel and Mushroom Soup over a large spoonful of Toasted Quinoa.
Thank you, Farideh Sadeghin for inspiring this recipe.
Here’s the order I recommend for preparing Caramelized Onion Fennel and Mushroom Soup:
- Begin by making the Rich Mushroom Stock (can be made and refrigerated up to 3 days in advance).
- Slice and caramelize the onions and fennel (this can be completed up to a few days in advance).
- Prepare the soup.
- Make the Toasted Quinoa about 45-60 minutes before you’ll serve the soup.
Makes 10 cups of soup Printer-Friendly Recipe
Active time 75 minutes, if you make your own stock
Total time 2 hours, if you make your own stock
Ingredients
2 tablespoons olive oil
2-3 yellow onions, sliced ⅛th -inch thick (6 cups)
¾-1 pound bulb fennel, trimmed, halved, sliced ⅛th inch thick lengthwise (5-6 cups), reserving the fronds for garnish
2 large cloves garlic, pressed or minced
8 cups unsalted, homemade Rich Mushroom Stock or purchased
2 large sprigs fresh thyme
2 bay leaves
1 tablespoon sea salt (less if using seasoned broth)
Dozen twists freshly ground pepper
1 pound mixed mushrooms, i.e., cremini, shiitake, portobello, Asian mix, etc. 3 cups thinly sliced, the rest coarsely chopped
Salt and pepper to taste
Toasted Quinoa (optional) ⅓ cup per each cup of soup
Garnish:
1 cup chopped fresh parsley, chives or scallions, fennel fronds
Instructions for Caramelizing Onions and Fennel
- Heat 2 tablespoons oil in a large sauté pan over
medium-low heat. When hot stir in the sliced onion and fennel. Cover the pan and cook for 10 minutes, stirring once. - Uncover the pan and raise the heat to medium. Toss the onions and fennel. Sprinkle them with a large pinch of salt. Every 3-5 minutes, turn the onions over, scraping up the bottom of the pot, as necessary. After 15 minutes, lower the heat to medium low.
- Now begin turning the onions over and scraping the bottom of the pot about every 5-10 minutes or sooner to make sure they don’t start to stick or burn. The onions will go from golden brown to darker and darker shades of brown and will have reduced significantly in volume. The entire process usually takes about an hour.
- Once the onions and fennel have caramelized, stir in the
garlic. Cook until fragrant. - Blend in the Rich Mushroom Stock, fresh thyme, bay leaves, salt and freshly ground pepper. Bring the soup to a boil, then reduce the heat to medium low, so it simmers.
- While the soup simmers, place a 12-inch sauté pan over high heat. Add the coarsely chopped and sliced mushrooms. Cook, stirring
occasionally, about 10 minutes until the mushroom juices have evaporated and the mushrooms have browned. - Transfer the mushrooms into the soup. If the mushrooms stuck at all, add a ladle full of the soup stock to deglaze—stir up any brown bits from the bottom—the pan. Then add everything back into the soup. Cook the soup another 5 minutes. Adjust the seasoning to
taste. - Serve Caramelized Onion Fennel and Mushroom Soup garnished with coarsely chopped fresh fennel, parsley and chives or scallions.
- Or, for a heartier bowl of soup, put about ⅓ cup of Toasted Quinoa in the bottom of each bowl and top with the soup. Garnish with the fresh herbs.