1. Trim beets (reserve greens for another use) and peel. Separately cut golden and red beets into 1/4-inch-thick slices. Finely chop onion. In each of two 3-quart saucepans melt 1 tablespoon butter over moderate heat. Add red beets and half of onion to butter in one pan and golden beets and remaining onion to other. Cook beet mixtures, stirring, 5 minutes. Add 2 cups water and 1 teaspoon salt to each beet mixture and simmer, uncovered, 40 minutes, or until beets are very tender.
2. In a blender or food processor puree each mixture separately with 1 1/4 cups milk until smooth (use caution when blending hot liquids). Return soups to pans and reheat over moderate heat.
3. In a small bowl whisk together creme fraiche or sour cream and dill. Divide soups among 6 bowls, pouring them simultaneously into opposite sides of each bowl.
4. Serve soup topped with cream mixture and garnished with dill.

Yield: 6 servings