Boil the Cabbage: Bring a large stock pot of water to a boil, add the whole cabbage, and simmer for 9 minutes, turning the cabbage once halfway through because it will float.Remove it from the pot and place it in a colander to cool. Separate the Leaves: When the cabbage is cool enough to handle, use a pairing knife to cut around the base of the stem and gently release the leaves from the head. Keep the leaves as intact as possible and set aside at least 10 large leaves for rolling. Prepare Additional Leaves: Set aside any torn or extra cabbage leaves to line the baking dish or use separately. If the inner leaves near the core are too firm, soften them individually in the hot water as needed, or refrigerate the remaining cabbage for another recipe. Rehydrate the Porcini: Place the dried porcini mushrooms in a bowl, pour 2 cups (472 g) of the very hot cabbage-cooking water over them, cover, and let them rehydrate for 30 minutes.
Reserve the Mushroom Liquid: Strain the rehydrated porcini, reserving the soaking liquid. Squeeze as much liquid as possible from the mushrooms, then roughly chop them and set aside. Cook the Rice and Lentils: Bring 1 1/2 cups (454 g) water to a boil in a small saucepan. Add 1/4 tsp salt, the bay leaf, lentils, and brown rice. Reduce the heat to low, cover, and cook for about 35–40 minutes, until the rice and lentils are tender. The lentils may finish cooking before the rice, which is acceptable for the filling. Sauté the Cremini Mushrooms: Heat 2 Tbsp olive oil in a nonstick sauté pan until shimmering.Add the sliced cremini mushrooms, stir well, then allow them to cook for about 2 minutes before stirring again. Continue cooking this way for approximately 13–14 minutes, allowing the mushrooms to develop a good sear. Add the Shallots: Add the chopped shallots to the sauté pan about 3 minutes before the mushrooms have finished cooking, and continue cooking with the mushrooms.
Process the Mushroom Filling: Transfer the cooked mushroom mixture to a food processor. Add the chopped porcini, breadcrumbs, 1 tsp tomato paste, 1/2 tsp salt, and the fresh thyme leaves from about 7 stems.Pulse about 4 times, scrape down the bowl, and pulse a few more times until the mixture comes together while remaining textured rather than pasty. Combine the Filling: When the rice and lentils are tender, add the processed mushroom mixture to the saucepan containing them. Add about 1/2 tsp ground black pepper, stir thoroughly, and taste for seasoning adjustment. Set the finished filling aside. Make the Tomato Sauce: Return to the same sauté pan used for the mushrooms and pour in the reserved porcini soaking liquid. Simmer over medium heat for about 2 minutes, allowing the liquid to reduce slightly. Finish the Sauce: Stir the remaining tomato paste into the reduced mushroom broth until dissolved. Add 1/4 tsp salt and a few grinds of black pepper, then stir in the diced tomatoes. Cook over low heat for about 2–3 minutes, then set the sauce aside. Preheat the Oven: Preheat the oven to 350°F (180°C) and lightly coat a large casserole dish with pan spray.
Line the Baking Dish: Cover the bottom and most of the sides of the casserole dish with 3–4 cabbage leaves, or enough leaves to create a lining. If the leaves extend over the edges, leave them as they are; cut a small notch at the base of each stem if necessary to help the leaves lie flat. Prepare the Rolling Leaves: Check the remaining cabbage leaves and cut a small notch from any thick stem that feels too tough to roll easily.
Fill the Cabbage Leaves: Place about 1/4 cup (40 g) of the mushroom filling near the base of each cabbage leaf, adjusting the amount for smaller leaves.
Roll the Cabbage: Fold the sides of each leaf inward, then roll it up gently, tucking in the sides as needed to enclose the filling.
Arrange the Rolls: Place each cabbage roll seam-side down in the prepared casserole dish on top of the cabbage leaves. Continue filling and rolling until all the filling is used. The rolls may be arranged closely together, but they should not overlap; use a second lined baking dish if necessary. Add the Tomato Sauce: Pour the prepared tomato sauce over and around the cabbage rolls.The sauce should reach approximately halfway up the sides of the rolls rather than completely submerging them. Adjust the Moisture: Drizzle dry white wine and/or vegetable broth over the top as needed, following the original preparation.
Season the Rolls: Add several grinds of black pepper and a pinch of salt over each roll. Lay 5–6 fresh thyme sprigs across the top.
Bake the Cabbage Rolls: Bake uncovered at 350°F (180°C) for 40–50 minutes, until the tops are lightly golden and some areas have become slightly crisp.
Rest and Finish: Remove the baking dish from the oven, discard the crispy thyme leaves, and let the rolls stand for 5 minutes before serving. Sprinkle fresh thyme over the top just before serving. Store the Rolls: Transfer leftovers to a lidded container and refrigerate for up to 2 days.
Prepare Ahead: For a make-ahead meal, assemble the cabbage rolls one day in advance without preparing the sauce.Cover the rolls in the casserole dish and refrigerate. The following evening, prepare the tomato sauce and bake the rolls according to the instructions above.
