Before you start, ensure you have these things done and set aside:Grate the butter and put in the freezer until you need it.Mix the buttermilk, heavy cream, vanilla extract and sourdough starter together in a jug. Now in a small mixing bowl, add together the all purpose flour, baking powder, salt and sugar. Stir together until well combined.
Now put the cold, grated butter into the flour mixture and rub it into the flour. You won't need to rub it a lot because the butter is grated, so as long as it's well distributed and coated in flour it will be fine.
Now, pour the buttermilk mixture (wet ingredients) into the dry ingredients and stir together to form a wet dough.
Scoop the wet dough and place blobs onto the top of the berry filling you prepared earlier. It doesn't have to be neat, just blob it on. It's good to have some of the filling visible too as this will bubble up during cooking and be so pretty!
Sprinkle the top of the sourdough berry cobbler with the granulated sugar.
Bake the sourdough berry cobbler in the oven at 200C (390F) for 40 minutes. You'll know it's ready when the topping is golden brown and you can see the filling bubbling up around the sides.
Remove from the oven and allow it to sit for around 10 minutes before serving. This allows the filling to thicken and become nice and jammy.