Melt the butter and let it cool down slightly.
Combine sugar, flour, soda and vanilla sugar in a bowl and mix. Pour the melted butter over and mix into a crumble.
Set ⅓ of the crumble aside.
Add the buttermilk/natural yogurt/sour cream and the egg in with the rest of the crumble. Mix into a smooth batter. I like using hand whisk for this but I don't whisk it as such. It doesn't matter if there are some crumbly bits left in the dough.
Line the dish with baking parchment and pour the batter into it. Sprinkle with the berries and lastly the crumble you set aside.
Bake at 200° C for approximately 30 minutes until golden brown. If you can see the dough is still loose in the middle when you move the dish, add 5 minutes to the baking time or bake until the pie is completely set. 30 minutes was enough in my oven.
