This oversize red, white, and blue cobbler is designed to feed a Fourth of July party crowd. Crystallized ginger adds a little zing to a standard cobbler topping. Although this is a classic summer cobbler, it can be made successfully out of season with frozen berries (no need to thaw). The recipe is easily cut in half; bake it in a 9-inch deep-dish pie plate for forty to forty-five minutes. Crystallized ginger is fresh ginger that has been dried and preserved in sugar. Good-quality crystallized ginger should not be fibrous, and it should be moist and tasty enough to eat out of the bag.
For the fruit filling
3-1/3 cups (about 21 oz.) fresh blueberries
3-1/3 cups (about 21 oz.) fresh blackberries
3-1/3 cups (about 21 oz.) fresh raspberries
1 cup plus 2 Tbs. granulated sugar (depending on the ripeness of the berries)
1-1/8 tsp. coarse salt
2 tsp. freshly squeezed lemon juice (from 1 lemon)
6 Tbs. cornstarch
For the biscuits
2-2/3 cups all-purpose flour
2/3 cup granulated sugar
1 Tbs. baking powder
2 tsp. baking soda
1 tsp. coarse salt
1/2 cup diced crystallized ginger
12 Tbs. (1-1/2 sticks) cold unsalted butter, cubed
1/2 cup buttermilk
1 Tbs. sanding sugar, for finishing
Make the filling
In a large bowl, toss together the blueberries, blackberries, raspberries, granulated sugar, salt, lemon juice, and cornstarch. Transfer to a 10 by 14-inch rectangular, ceramic baking dish.
Make the dough and bake the cobbler
Set the oven rack in the lower third of the oven. Preheat the oven to 375°F. Line a baking sheet with parchment paper or a nonstick silicone baking mat.
In a large bowl, whisk together the flour, granulated sugar, baking powder, baking soda, salt, and crystallized ginger.
Working quickly so as not to warm the butter, work the butter into the flour mixture with your fingers until it resembles coarse crumbs. Add 6 Tbs. of the buttermilk and fold with a rubber scraper or your hands until the buttermilk has been absorbed and there are no dry patches. Add the remaining 2 Tbs. of buttermilk as necessary (you won’t use all of it; reserve what’s left for brushing the dough). The dough should be dry enough to hold a shape when you cut it out.
Turn the dough out onto a lightly floured work surface. With lightly floured hands, pat the dough to about 3/4 inch thick. Cut out twelve stars with a 3-3/8-inch (measuring point to point) star cookie cutter and place them in a single layer on top of the fruit. Brush the stars with the reserved buttermilk, and sprinkle each with 1/4 tsp. of sanding sugar. Bake, rotating the baking sheet two-thirds of the way through the baking time, until the biscuit topping is lightly browned and cooked through, 60 to 65 minutes. Serve warm or at room temperature.