ine a sieve or colander with cheesecloth and set over a bowl, leaving at least 1/2-inch clearance from the bottom. (Alternatively, use a coffee filter lined with filter paper.) Spoon in yogurt, cover and let drain in the refrigerator for 1 hour. Discard whey.
Whip cream in a small bowl until soft peaks form. Add sugar, if using, and continue whipping until firm peaks form. Fold in drained yogurt.