Place 4 tablespoons of unsalted butter into a 10-12-inch cast iron skillet and place in the oven. Preheat oven to 350℉.
Add the frozen berries, brown sugar, and corn starch to a large bowl. Stir to coat all of the berries. Set aside.
While the butter is melting, make the biscuits. Add the flour, baking powder, ¼ cup brown sugar, salt, and blended cottage cheese to a bowl. Using a silicone spatula, stir until a ball starts to form. Then, switch to your hands and knead until a ball forms.
Once the butter has melted, remove the skillet from the oven. Transfer the berries to the bottom of the pan. Break the cobbler biscuit dough into biscuit-looking pieces and place them on top of the mixed berries.
Whisk an egg and brush it across the top of the biscuits, then top with the remaining brown sugar.
Bake for 30 minutes. Remove from the oven and allow to cool for 10 minutes before serving.