It's a classic! There's nothing like cobbler for comfort food on a cool evening.
Preheat oven to 375 degrees.
In a large bowl, combine 2/3 cup sugar and cornstarch; mix well.
Add raspberries; toss to coat.
Transfer mixture to an 8 or 9 inch glass baking dish or shallow 1-1/2 quart casserole dish.
In a small bowl, combine flour, baking soda, and salt.
In a bowl of an electric mixer, beat together butter and remaining 1/3 cup sugar until light and fluffy.
Beat in egg white.
On low speed, beat in half of flour mixture.
Beat in buttermilk, then remaining flour mixture.
Drop batter by heaping tablespoons into eight mounds over raspberries.
For topping, combine sugar and cinnamon; sprinkle over batter.
Bake 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.
Serve with ice cream or frozen yogurt and garnish with mint if desired.