Slice onion thin, heat 4 tbsp butter in large skillet with cover. Add onions, reduce heat to low and cover until they nearly dissolve. Cut greens into small pieces and add to onions. Should more than fill the pan (you can add more as they wilt). Cover and cook 10-15 min, remove cover and cook another 10-15 min. Preheat oven to 400. Grease a baking dish with one tsp. butter, sprinkle salt, pepper, flour over the greens and stir. Increase heat to high, stirring, then add milk a little at a time, making a sauce. When it has thickened (about 5 min.) spread mixture into baking dish. Mix cheese (calls for gruyere or parmsan) and breadcrumbs together and sprinkle over the top, cover with remaining butter and bake about 20 min.