Preheat oven to 425 degrees F. Trim and core fennel bulbs, reserving some of the leafy tops. Cut each fennel bulb in thin wedges; set aside. Sprinkle pork with rosemary, fennel seed, 1 teaspoon salt, and 1/4 teaspoon black pepper. In 12-inch straight-sided oven-going skillet brown pork on all sides in hot oil. Remove pork from pan; set aside.
Add fennel, onion, and garlic to skillet; cook 4 minutes or until lightly browned, stirring occasionally. Remove skillet from heat; add broth, vermouth, and sour cream. Return to heat. Bring to boiling. Return pork to pan; transfer to preheated oven.
Roast, uncovered, 25 to 30 minutes or until slightly pink in center (155 degrees F). Serve pork with vegetables and juices. Top with reserved fennel tips and rosemary. Pass additional sour cream sprinkled with rosemary. Makes 8 servings.