Cut any large potatoes in half. In a 4-quart Dutch oven combine potatoes, turkey, broth, and leek. Bring to boiling; reduce heat. Simmer, covered, for 15 minutes.
In a small bowl stir together cream and mustard; add to Dutch oven along with lemon thyme. Simmer, uncovered, about 5 minutes more or until potatoes are tender, stirring occasionally. Top each serving with 1/4 cup cabbage.