3 cups frozen dark sweet cherries (14 oz; not thawed)
1/4 cup sugar
2 teaspoons cornstarch
Scant 1/4 teaspoon cinnamon
3/4 cup all-purpose flour
1 tablespoon sugar
1/4 teaspoon baking soda
1/4 teaspoon baking powder
1/8 teaspoon salt
1 1/2 tablespoons cold unsalted butter, cut into small bits
1/3 cup well-shaken low-fat buttermilk
Cook all filling ingredients with a pinch of salt in a 2-quart heavy saucepan over moderate heat, stirring occasionally, until sugar begins to dissolve, about 3 minutes. Spoon filling into a 9-inch ceramic or glass pie plate (1 inch deep).
Make topping and bake cobbler:
Whisk together flour, 2 teaspoons sugar, baking soda, baking powder, and salt in a medium bowl. Blend in butter with your fingertips or a pastry blender until mixture resembles coarse meal. Stir in buttermilk with a fork until just combined (do not overmix).
Drop dough in 4 mounds over filling, leaving space between mounds. Sprinkle topping with remaining teaspoon sugar.
Bake until topping is golden brown and fruit is bubbling, about 25 minutes. Cool slightly and serve warm.