Remove and discard large leaves and tough ends of stalks from broccoli. Cut away tops, and coarsely chop. Peel and coarsely chop stems.
Cook broccoli in boiling, salted water to cover 8 minutes or until crisp-tender; drain.
Process cooked broccoli and Crème Fraîche in a food processor or blender until smooth, stopping to scrape down sides.
Stir together broccoli mixture, cheese, and next 4 ingredients. Pour mixture into a lightly greased 2-quart baking dish. Dot with butter.
Bake at 350° for 25 minutes or until thoroughly heated. Serve casserole immediately.