Toss together chopped dandelion, chopped onion and fried bacon pieces. Set aside. In skillet warm butter and cream until butter melts. Beat egg and then add salt, pepper, vinegar, sugar and flour. Blend the egg mixture into the slightly warm cream mixture. Increase heat and cook, stirring constantly until the mixture thickens. Pour hot dressing over the greens and toss gently. Serve at once. Gather the dandelion leaves early in the spring before the plants flower or they will be bitter.