Mix beef, thyme, orange peel strips, salt, pepper, and wine in a bowl. Cover and chill, stirring occasionally, at least 4 hours or overnight.
Bring 2 cups beef broth to a boil and pour over porcini in a bowl. Let stand until mushrooms are soft, about 20 minutes. Lift mushrooms out and coarsely chop. Reserve soaking liquid.
Meanwhile, pour beef and marinade into a strainer set over a bowl. Discard thyme sprigs and orange peel strips; reserve marinade. Dry beef on paper towels.
Cook pancetta in a large, heavy pot over medium-high heat, stirring often, until browned and crisp, 5 to 8 minutes. Lift out with a slotted spoon. Add beef in batches and cook, turning pieces, until well browned all over, 7 to 8 minutes per batch. If you need more fat in the pot, add oil between batches. Transfer beef to a large bowl as browned. Add shallots to pot and cook, stirring often, until browned, about 5 minutes. Transfer to another bowl.
Return pancetta and beef to pot and add reserved marinade, mushroom-soaking liquid (pour in carefully, leaving sediment behind), and mushrooms. Liquid should just cover meat; add a little more broth if necessary. Cover and simmer, gently stirring occasionally, about 2 hours. Add the shallots and grated orange peel and continue simmering, uncovered, until beef is very tender when pierced, about 30 minutes longer.