Adapted from Smitten Kitchen
3 tablespoons olive oil
3 tablespoons butter, softened
2 (20-ounce) containers or 2 1/4 pounds, mixed or cremini mushrooms (not white button), cut in 1/4-inch slices
1 teaspoon kosher salt, divided, plus more to taste
1 carrot, finely diced
1 small yellow onion, finely diced
2 cloves garlic, minced
1 cup full-bodied red wine such as a French Malbec
2 cups beef or vegetable broth
2 tablespoons tomato paste (I like to, at times, use 3 depending on the flavor/potency of the tomato paste)
4 sprigs fresh thyme
1 1/2 tablespoons all-purpose flour
1 cup pearl onions, peeled (thawed if frozen)
Egg noodles, or cooked barley for serving
Chopped parsley, for garnish, optional
Sour cream, for garnish, optional
In an 8-quart Dutch oven or heavy stock pot set over high heat, warm the 1 tablespoon of the olive oil and 1 tablespoon of butter until the butter starts to foam. Add half of the mushrooms, and cook, without moving, until they begin to darken, but not yet release any liquid — 3 to 4 minutes. Transfer to a bowl and set aside. Add another tablespoon of olive oil and another tablespoon of butter and repeat the searing with the second batch of the mushrooms. Transfer to a bowl and sprinkle with 1/2 teaspoon of salt. [I recommend using a wider pot for the searing and cooking here because you want the mushrooms to have enough room to brown. If you use a smaller pot, you’ll crowd the mushrooms and instead of searing, they will steam and you’ll wind up with a less flavorful dish.
2. Lower the heat to medium and add the last tablespoon of olive oil. Add the carrots, onions, thyme, 1/2 teaspoon of salt, and several grinds of black pepper into the pan, and cook, stirring occasionally, until the onions are lightly browned between 7 and 10 minutes. Add the garlic and cook, stirring, for 30 seconds.
3. Pour in the wine, scraping any stuck brown bits off the bottom (it’s called a fond), then return the heat back to high and cook until the wine is reduced by one half, about 5 minutes. Stir in the tomato paste and the broth. Add back the mushrooms, with any juices that have collected at the bottom of the bowl, and the pearl onions, and once the liquid comes to a boil, decrease the heat to low so the mushrooms simmer. Cook, uncovered, until the mushrooms are very tender, and the onions are soft, sunken, and enveloped in the sauce, about 25 minutes. Taste the sauce and adjust seasonings.
4. Using a fork, combine the remaining butter with the flour until it is one uniform mass, and stir it into the stew. Let the stew simmer 10 more minutes until the sauce is the consistency of gravy. If the sauce is too thin, simmer it in 5 minute increments to reduce to the right consistency. Fish the thyme sprigs out and discard them. Serve over cooked egg noodles or barley with a dollop of sour cream, if you like, and a sprinkling of parsley.