Short Rib Sauce
- 5 fresh thyme sprigs plus 1 tablespoon chopped fresh thyme
- 1/2 ounce dried porcini mushrooms
- 4 pounds meaty beef short ribs
- 4 tablespoons olive oil, divided
- 4 medium carrots, chopped
- 2 tablespoons tomato paste
- 2 cups dry red wine (such as Cabernet Sauvignon or Zinfandel)
- 2 1/2t cups low-salt beef broth
- 5 tablespoons unsalted butter
- 1/4 cup all purpose flour
- 1/2 teaspoon freshly grated nutmeg
- 2 cups freshly grated Parmesan cheese
- 18 5 3/4x3 1/2-inch sheets no-bake lasagna noodles (from two 9-ounce packages)
Short Rib Sauce
Tie all herb sprigs and bay leaf in cheesecloth for bouquet garni; trim excess cheesecloth. Set bouquet garni aside. Place mushrooms in heatproof bowl. Add 1 cup boiling water; cover and let stand until mushrooms soften, about 20 minutes. Using slotted spoon, transfer mushrooms to work surface; chop. Reserve mushroom soaking liquid.
Meanwhile, preheat oven to 325°F. Sprinkle ribs with salt and pepper. Place flour in medium bowl. Dredge ribs in flour, shaking off excess; place on rimmed baking sheet. Reserve flour. Heat 2 tablespoons oil in heavy large skillet over medium-high heat. Working in batches, cook ribs until browned on all sides, about 6 minutes per batch. Return ribs to baking sheet.
Heat remaining 2 tablespoons oil in heavy large pot over medium heat. Add carrots, celery, and onion; cook until softened, stirring often, about 10 minutes. Stir in chopped mushrooms. Sprinkle 1 tablespoon reserved flour over vegetables (discard remaining flour). Add tomato paste; stir until tomato paste begins to brown on bottom of pot, about 1 minute. Add Port and stir until almost all liquid is absorbed, scraping up any browned bits, about 1 minute. Add red wine. Pour in reserved mushroom soaking liquid, leaving any sediment behind. Bring to boil; simmer until reduced by about 1/3, stirring often, about 7 minutes. Add broth, garlic, and bouquet garni. Return to boil. Return ribs to pot, arranging meat side down in single layer. Cover pot; place in oven and braise ribs until very tender, about 2 1/4 to 2 1/2 hours.
Using tongs, transfer ribs from pot to rimmed baking sheet to cool. Discard bouquet garni. Shred beef; discard bones. Spoon off fat from top of sauce in pot; discard fat. Boil sauce until reduced to 51/2 cups, about 8 minutes. Return meat to sauce. Season sauce to taste with salt and pepper. Stir in chopped thyme. DO AHEAD Can be made 3 days ahead. Cool slightly. Refrigerate uncovered until cold, then cover and keep chilled.
Melt butter in heavy large saucepan over medium heat. Add flour; whisk until smooth. Cook until light golden brown, whisking frequently, about 6 minutes. Add milk; bring to boil, whisking constantly. Boil 1 minute. Add nutmeg. Season béchamel to taste with salt and pepper. DO AHEAD Can be made 1 day ahead. Cool slightly; cover and chill.
Preheat oven to 375°F. Butter 15x10x2-inch baking dish. Spoon 1 cup meat sauce over bottom of dish; spread in thin layer. Sprinkle 2 tablespoons cheese over. Arrange 6 lasagna noodles over to cover (noodles may overlap slightly). Drizzle 1 cup béchamel over noodles, spreading in even layer; sprinkle 1/4 cup cheese over. Spread 2 cups meat sauce over. Repeat with noodles, béchamel, cheese, and meat sauce. Cover with remaining 6 noodles. Spread remaining béchamel over noodles. Sprinkle remaining cheese over.
Bake lasagna uncovered until edges are bubbling and top is golden brown in spots, about 45 minutes. Let rest 10 minutes.