Stir together fresh blueberries, lemonade concentrate, and 1/2 cup cold water in a 3-qt. saucepan. Bring to a boil; reduce heat, stir in dried lavender, and simmer, stirring occasionally, 5 minutes or until blueberries burst. Remove from heat, and cool 5 minutes. Stir in vanilla extract.
Press mixture through a fine wire-mesh strainer into a large bowl, using back of a spoon to squeeze out juice. Discard pulp. Stir in yogurt. Cover and chill 4 to 24 hours. Serve with Sweet Treat Croutons.
*2 (12-oz.) packages frozen blueberries may be substituted.