Cut potatoes in small cubes, add chopped egg whites and onions. Mash egg yokes, add mustard, salt and pepper. Mix thoroughly and add vinegar. Heat cream to boiling point and pour slowly on egg mixture. Add butter. When butter is melted pour mixture over potatoes. Add mayonaise and chopped bacon and mix carefully. Cool and serve. Garnish with grated carrots, parsely, and a red radish in the middle.