Preparation Heat oil in heavy large pot over medium-high heat. Add onions, carrots, thyme and bay leaf. Sauté until tender, about 10 minutes. Add 4 1/2 cups broth and wine. Bring to boil. Reduce heat; cover pot partially. Simmer 40 minutes, stirring occasionally and skimming off fat if necessary. Strain into 4-cup glass measuring cup, pressing on solids; discard solids. Add more broth if necessary to measure 4 cups, or return broth to pot and boil until reduced to 4 cups. (Can be made 1 day ahead. Cool to room temperature. Cover; chill.) Position rack in bottom third of oven and preheat to 325°F. Place roasting rack in shallow roasting pan. Sprinkle pork generously with salt and pepper. Set pork, fat side up, on rack in roasting pan. Roast until thermometer inserted into thickest part of pork registers 180°F, about 3 hours. Transfer to cutting board. Tent with foil. Scrape pan juices into 1-cup glass measuring cup. Spoon off fat. Reserve juices. Melt 2 tablespoons butter in heavy large skillet over medium heat. Add all mushrooms. Cover and cook until tender, stirring often, about 10 minutes. Pour pan juices and 4 cups broth into mushrooms. Bring to simmer. Mix 4 tablespoons butter and flour in small bowl to form paste. Add mustard. Gradually whisk paste into skillet. Cook until gravy thickens slightly, whisking occasionally, about 5 minutes. Serve pork with gravy.
Preparation Heat oil in heavy large pot over medium-high heat. Add onions, carrots, thyme and bay leaf. Sauté until tender, about 10 minutes. Add 4 1/2 cups broth and wine. Bring to boil. Reduce heat; cover pot partially. Simmer 40 minutes, stirring occasionally and skimming off fat if necessary. Strain into 4-cup glass measuring cup, pressing on solids; discard solids. Add more broth if necessary to measure 4 cups, or return broth to pot and boil until reduced to 4 cups. (Can be made 1 day ahead. Cool to room temperature. Cover; chill.) Position rack in bottom third of oven and preheat to 325°F. Place roasting rack in shallow roasting pan. Sprinkle pork generously with salt and pepper. Set pork, fat side up, on rack in roasting pan. Roast until thermometer inserted into thickest part of pork registers 180°F, about 3 hours. Transfer to cutting board. Tent with foil. Scrape pan juices into 1-cup glass measuring cup. Spoon off fat. Reserve juices. Melt 2 tablespoons butter in heavy large skillet over medium heat. Add all mushrooms. Cover and cook until tender, stirring often, about 10 minutes. Pour pan juices and 4 cups broth into mushrooms. Bring to simmer. Mix 4 tablespoons butter and flour in small bowl to form paste. Add mustard. Gradually whisk paste into skillet. Cook until gravy thickens slightly, whisking occasionally, about 5 minutes. Serve pork with gravy.