Place a small roasting pan in oven. Preheat oven to 425°.
Sprinkle pork evenly with 1/2 teaspoon salt and pepper. Add 1 tablespoon olive oil to preheated pan, and swirl to coat. Add pork to pan. Roast at 425° for 20 minutes or until a thermometer inserted in the thickest portion of pork registers 145°, turning after 10 minutes. Remove pork from pan, and let stand for 10 minutes.
Place roasting pan over medium-high heat. Add the remaining 1 tablespoon oil to pan; swirl to coat. Add mushrooms; sauté 4 minutes, stirring occasionally. Add garlic, and sauté 1 minute, stirring constantly. Stir in vinegar, and bring to a boil, scraping pan to loosen browned bits. Cook 1 minute or until liquid almost evaporates, stirring occasionally. Stir in remaining 1/4 teaspoon salt and broth; bring to a boil. Cook until liquid is reduced to 1/3 cup (about 7 minutes). Remove from heat, and stir in crème fraîche and mustard. Cut pork crosswise into slices. Place 3 ounces pork on each of 4 plates, and top each serving with about 2 1/2 tablespoons sauce. Garnish with parsley.