Warming, savory and super-flavorful, this good-for-ya stew is perfect healthy comfort food for winter. It's a real umami powerhouse and tastes about as meaty as vegetarian food gets. To make this recipe vegan, replace the butter with an additional 2 tablespoons olive oil and omit the cream.
Warm 1 tablespoon each of the olive oil and butter over medium-high heat in a 5 quart Dutch oven or other heavy lidded pot. Add mushrooms and cook, stirring just a few times, until nicely browned and reduced in volume by half. Remove mushrooms to a bowl and set aside.
In the same pot, heat the remaining butter and olive oil. Add onion, celery, carrots and 1/2 teaspoon of the salt and cook, stirring occasionally, until beginning to soften, about five minutes. Add the garlic and cook, stirring frequently, for a minute. Stir in the tomato paste and cook a minute more.
Add the vegetable broth, remaining 1/2 teaspoon salt, soy sauce, marmite, bay leaf and thyme. Raise heat to high. Rinse and drain the lentils and add to pot. When broth comes to a boil, reduce heat, cover, and simmer for about 30 minutes, until lentils are nice and tender. Remove from heat and remove thyme stems and bay leaf.
If you have an immersion blender, pulse it 4 or 5 times to puree the stew just a little bit. (Alternatively, transfer about two cups of the stew to a blender and puree it, then return to pot, or simply forego this step if you prefer.)
Return the mushrooms and any accumulated juices to the pot along with the spinach and cream. Simmer briskly, uncovered, until spinach is wilted, about two minutes. Off the heat, stir in vinegar. Let sit for 10 minutes, then ladle into bowls and serve with good bread.
*Brown lentils are sometimes called green lentils. (Just don't confuse them with green split peas, which are a different thing entirely. Green split peas are bright green and glossy and not what we're looking for here.)