In a heatproof bowl, soak the morels in the boiling water until softened, about 30 minutes. Remove and rinse under running water, rubbing to loosen any grit. Let the soaking liquid stand.
Season the veal with salt and pepper, then dust with flour. In a very large skillet, melt 1 tablespoon of the butter in the oil. Add the veal and cook over high heat until browned on the bottom, 2 to 3 minutes. Turn and cook until browned on the bottom and the meat is just pink inside, about 2 to 3 minutes. Transfer the veal to a warmed platter and cover loosely with foil.
Melt the remaining 1 tablespoon of butter in the same skillet. Add the garlic,shallots and thyme and cook over low heat, stirring, until softened, about 3-5 minutes. Add the wine and boil, scraping up any browned bits from the bottom, until almost evaporated, about 4 minutes. Add the morels and their liquid, leaving any grit behind. Cover and simmer over low heat until the morels are softened, about 5 minutes. Add the chicken stock and any veal juices and simmer over moderately high heat until reduced by half, about 5 minutes. Add the creme fraiche and simmer until thickened, about 4 minutes. Add the lemon juice and season with salt and pepper.
Return the veal medallions to the skillet and simmer for 1 minute, turning once. Transfer the veal and sauce to a platter or plates. Discard thyme. Garnish with scallions.