1Preheat oven to 375 degrees.
2In a large bowl, combine 2/3 cup sugar and cornstarch; mix well.
3Add raspberries; toss to coat.
4Transfer mixture to an 8 or 9 inch glass baking dish or shallow 1-1/2 quart casserole dish.
5In a small bowl, combine flour, baking soda, and salt.
6 In a bowl of an electric mixer, beat together butter and remaining 1/3 cup sugar until light and fluffy.
7Beat in egg white.
8On low speed, beat in half of flour mixture.
9Beat in buttermilk, then remaining flour mixture.
10Drop batter by heaping tablespoons into eight mounds over raspberries.
11For topping, combine sugar and cinnamon; sprinkle over batter.
12Bake 35 to 40 minutes or until fruit is bubbly and topping is golden brown. Transfer to a wire cooling rack; let stand at least 30 minutes.
13Serve with ice cream or frozen yogurt and garnish with mint if desired.
Source: Rosby's Berry Farm, Brooklyn Heights, Ohio, at www.rosbys.com