Preheat oven to 375 degrees. Place oven racks in middle and bottom. Line a baking sheet with aluminum foil and place on bottom rack to catch any juices that might bubble over.
FILLING: In a large bowl, stir together berries, sugar, cornstarch, salt, and lemon juice. Transfer to a 2 1/2-quart baking dish.
TOPPING: Whisk together flour, sugar, baking powder and salt. Cut in butter with a pastry blender, until the largest pieces are the size of small peas. Pour in cream, stirring until a soft sticky dough forms. Divide dough evenly into 9 pieces (about 1/4 cup each) and dollop over filling. Brush with cream and sprinkle with sugar.
Bake until biscuits are golden brown and filling is bubbling in the center, about 55-60 minutes. Cool at least 1 hour before serving. Serve warm or room temperature with a scoop of ice cream or drizzled with heavy cream, if desired.