Preheat oven to 350 degrees F (175 degrees C). Lightly grease a 9x9-inch pan.
Toss together frozen berries (do not thaw first), sugar, cornstarch, lemon juice, and salt. Pour into the prepared pan.
Mix together flour and yogurt in a medium bowl. Knead dough with your hands a few times until smooth. With lightly floured hands, divide dough into 9 pieces and press into flat disc shapes about 1/2 inch in thickness. Place dough evenly over berries. If desired, brush the top of each piece of dough with heavy cream and then sprinkle with turbinado sugar.
Place pan into preheated oven and bake until topping is browned, and the fruit mixture in the center of the pan is bubbling, 55 to 60 minutes. Allow to cool at least 20 minutes before serving.