Heat oven to 325°F. With sharp knife, make 6 cuts down center of roast, each 2 inches long and 2 inches deep. Stuff each cut with slices of onion; reserve any remaining onion. Place roast in ovenproof Dutch oven.
In small bowl, combine parsley, marjoram, rosemary and red pepper flakes; sprinkle evenly over top of roast. Insert meat thermometer into thickest part of roast without touching fat. Pour 1 3/4 cups of the broth around roast; cover and refrigerate remaining broth.
Place reserved onion slices, pepper and bay leaf in broth in Dutch oven. Arrange carrots and potatoes around roast; cover. Bake at 325°F. for 1 3/4 to 2 hours or until meat thermometer registers 160°F.
Remove roast from Dutch oven; place on serving platter. With slotted spoon, remove vegetables and arrange around roast; cover to keep warm.
Bring pan juices in Dutch oven to a boil. Boil 10 to 12 minutes or until reduced to half. Remove and discard bay leaf.
In small bowl, combine remaining broth and cornstarch; blend until smooth. Add to pan juices; cook and stir until mixture is bubbly and thickened. (If desired, gravy can be strained.) Serve gravy with roast and vegetables.