Vegetable Shepherd's Pie with Lentil & Porcini Filling

Soak the Mushrooms in 3 cups of hot water for at least 30 minutes. Meanwhile, in a medium saucepan, combine the brown lentils, 1 clove of garlic, kosher salt, and 4 cups of vegetable stock. Bring to a boil over medium-high heat, then reduce the heat to low and simmer, stirring occasionally, until the lentils are tender but not mushy, about 15–20 minutes. Drain the lentils in a colander, discarding the garlic clove.

Heat 3 Tbsp of olive oil in a large heavy pot or Dutch oven over medium heat. Add the diced onions and cook, stirring occasionally, until softened and translucent, about 12 minutes. Add the chopped garlic and cook until fragrant, about 1 minute. Stir in the tomato puree and cook, stirring constantly, until the tomato puree is caramelized and slightly darkened, about 2–3 minutes.

Add the bay leaves and dry white wine; stir, scraping up any browned bits from the bottom of the pot. Stir in the soaked mushrooms, then slowly pour the mushroom soaking liquid into the pot, being careful to leave any sediment behind. Bring to a simmer and cook until the liquid is reduced by half, about 10 minutes. Stir in the remaining 4 cups of vegetable stock and cook, stirring occasionally, until the sauce has reduced by half and slightly thickened, about 45 minutes.

Strain the mixture through a fine-mesh sieve into a large saucepan, discarding the solids (bay leaves and mushroom pieces). Bring to a boil. In a small bowl, stir together the cornstarch and soy sauce until dissolved into a smooth slurry. Add the cornstarch mixture to the saucepan and simmer, whisking constantly, until the sauce has thickened, about 5 minutes. Whisk in the chopped chives and season the sauce with kosher salt and pepper to taste.

Preheat oven to 450°F (232°C). In a large bowl, toss the potatoes, sage, 2 Tbsp of olive oil, 5 cloves of garlic, and rosemary sprigs; season with kosher salt and pepper to taste. Divide the mixture between 2 rimmed baking sheets in a single layer. Roast, stirring once halfway through, until the vegetables are tender and slightly browned, about 20–25 minutes. Transfer the roasted garlic to a small bowl, mash well with a fork, and stir into the prepared sauce. Discard the rosemary sprigs. The lentils, sauce, and roasted vegetables can be made up to 1 day ahead. Cover separately and refrigerate.

Arrange the cooked brown lentils in an even layer in a 3-qt baking dish. Toss the roasted vegetables with the sliced fresh mushrooms and chopped parsley, then layer this mixture evenly on top of the lentils. Pour the prepared sauce evenly over the vegetables.

Bake in the preheated oven until the potatoes are browned and the sauce is bubbly, about 30 minutes. Let stand for 15 minutes before serving. Garnish with additional fresh herbs, if desired. Serve hot.