Lemon juice; to taste Sugar; to taste Cut the tops off the beets, scrub them thoroughly, and put them in a saucepan with enough water to cover them by an inch and a little pinch of salt. Simmer the beets, covered, for 30 minutes if they're small, closer to 45 if large. They must be tender. Drain the beets, reserving the cooking liquid, and allow them to cool. When you can handle them, peel them and cut them into quarters or eighths. Combine the beets, raspberries, red onion, and 2 cups of the reserved cooking liquid, and puree it all in batches in a blender. Strain the puree through a sieve to remove the raspberry seeds. Stir in half cup of lemon juice, the balsamic vinegar, and 3 tablespoons of sugar. Stir until the sugar is dissolved, and taste. Add more lemon juice and more sugar only if needed, until the right sweet-sour balance is achieved. You might need a teensy pinch of salt, but be careful. Chill the soup in the refrigerator, and when it is completely cold, taste it again. Correct the seasoning if necessary. Serve in chilled bowls, with a spoonful of sour cream in the center of each one.