Watch the yogurt closely as it softens. It needs to be soft enough to stir easily into the raspberry mixture yet firm enough to hold the swirl.
Preheat oven to 350°.
Prepare brownie mix according to package directions, using a 13- x 9-inch baking pan. Bake at 350° for 20 minutes or until just set (brownies will be fudgy). Let cool completely.
Press raspberries through a fine sieve over a bowl, reserving 1 cup raspberry purée; discard seeds. Combine raspberry purée, sugar, cornstarch, and water in a saucepan; stir with a whisk until blended. Bring to a boil, and cook 1 minute or until thick, stirring constantly with a whisk. Pour raspberry sauce into a bowl; press plastic wrap onto surface of sauce, and let cool completely.
Add yogurt to raspberry sauce; swirl together, using a rubber spatula or spoon. Quickly spread yogurt mixture over brownies in pan. Cover and freeze 4 hours or until firm. Cut into 24 squares.
Oxmoor House Healthy Eating Collection