Turn this dessert into a quick and satisfying breakfast or lunch.
Toss together the blueberries, raspberries, and orange liqueur in a small bowl; set aside.
Combine the orange juice, sugar, and cornstarch in a small saucepan; add the blueberry mixture. Cook, stirring, until the mixture boils and thickens, about 1 minute. Remove the saucepan from the heat and let cool slightly.
Place a 1/2-cup scoop of the frozen yogurt into each of 4 goblets or dessert dishes. Spoon about 1/4 cup of the berry mixture on top and serve at once. Yields 1/2 cup frozen yogurt and 1/4 cup berry mixture per serving.
Spoon vanilla fat-free yogurt (not frozen) into a goblet, and alternately layer with the berry mixture and reduced-fat granola. Add fresh sliced peaches or nectarines, if you like.