Place about one third of the berries, including any that are less perfect (damaged, wilted, or soft) in the bowl of a food processor with the yogurt and sugar. Process until very smooth. (There still will be small seeds in the mixture; push the puree through a sieve or food mill fitted with a fine screen.)
Combine the remaining berries with the raspberry-yogurt sauce, and refrigerate until serving time (as long as 5 to 6 hours). Divide among four dessert dishes, and serve, garnished with mint or peppermint.
Variation: Don not combine the berries and sauce at the end. At serving time, divide the sauce among four dessert plates, and mound the berries in the center. Top each serving with a sprig of mint or peppermint and serve.
Core +1 Point for Sugar