Old-Fashioned Blackberry Cobbler

Ingredients

• For the filling:
• 7 ounces sugar
• 1 1/4 ounces tapioca starch
• 1/4 teaspoon Diamond Crystal kosher salt; for table salt, use about half as much by volume or the same weight
• 1/4 teaspoon ground cinnamon
• 1/8 teaspoon baking soda
• 32 ounces fresh blackberries
• 8 ounces fresh raspberries
• For the topping:
• 4 1/2 ounces all-purpose flour
• 1/2 ounce sugar
• 1 1/2 teaspoons baking powder
• 3/4 teaspoons Diamond Crystal kosher salt; for table salt, use about half as much by volume or the same weight
• 4 ounces cold unsalted butter, cut into 1/2-inch cubes
• 4 ounces cultured lowfat buttermilk or kefir, cold
• To Serve:
• Brown sugar or lemon whipped cream, optional

Directions

1. Set a rack in the lower middle of the oven and heat to 400 degrees F (205 degrees C). In a large bowl, combine the sugar with the tapioca starch, then whisk in the salt, cinnamon, and baking soda until everything is evenly blended. Add the berries and gently turn them through the mixture until coated. Transfer the fruit to a baking dish that measures 7 by 11 inches and is made of glass, ceramic, or stoneware; skip metal for this one. Set it aside while you make the topping.
2. For the topping, whisk the flour with the sugar, baking powder, and salt in a medium bowl. Add the butter and toss so the cubes separate, then press each piece flat between your fingers. Rub and pinch until the butter is in small, thin bits, more cornflake than cube. Using a flexible spatula, stir in the buttermilk. Drop the thick dough over the fruit in 1-tablespoon portions. If you like, scatter on additional sugar for crunchier tops.
3. Set the dish on a half-sheet pan lined with foil. Bake until the topping is golden and the fruit is bubbling hot in the very center, about 1 hour. Cool for at least 1 hour before serving so the filling can thicken; straight from the oven, it will be thin and loose. Cover leftovers with foil and store them at room temperature for 2 or 3 days.