This vegetable and fruit side dish makes a delicious accompaniment to our Prime Rib Roast.
Heat oven to 350 degrees. Juice lemon, place juice and both halves in large bowl of water. Peel quinces one at a time, halve, and core; transfer each half to acidulated water. Arrange quince halves, cut side up, in 8-by-13-inch roasting pan. Drizzle with 1 cup Madeira; season with 3/4 teaspoon salt and 1/4 teaspoon pepper. Pour 2 cups water into pan. Cover tightly with foil. Cook until tender and translucent, about 1 1/2 hours.
Meanwhile, place porcini mushrooms in bowl, cover with 1 cup boiling water; let stand until soft, about 30 minutes. Remove from water, reserving liquid; chop finely.
Heat butter in large saute pan over medium heat. Add onion; cook, stirring, until translucent, about 5 minutes. Add porcini mushrooms, thyme, and wild mushrooms; cook over medium heat, stirring until mushrooms release liquid, about 10 minutes. Reduce heat to medium low; add reserved porcini liquid, remaining 1/2 cup Madeira, 3/4 teaspoon salt, and 1/4 teaspoon pepper. Continue to cook over low heat until liquid is reduced to glaze and mushrooms are tender, 8 to 10 minutes. Transfer to large bowl.
Heat oven to 325 degrees. Cover each quince with mushroom mixture, so mixture almost spills over. Cover with foil; heat in oven 30 minutes until hot. Remove foil; bake 10 to 15 minutes. Serve garnished with thyme sprigs.