Mix the oatmeal, flour, sugar, baking soda and salt in a bowl.
Soda will make crumble even more crumbly and tender, but for the preparation of the traditional version of crumble to use it optional.
Add the butter to the dry mixture and RUB with your fingers all together into a crumb. Remove the bowl with the crumbs in the fridge while you prepare the filling.
If you think the crumbs are too much, you can put the excess in the freezer and use it another time. Frozen crumbs do not need to be defrosted – just sprinkle it over the berries.
Preheat the oven to 200°C.To prepare the filling, put the berries in a large bowl and gently mix them with the sugar, cornstarch and vanilla extract.
Put the berry mixture in a baking dish (20 cm in diameter).
Spread the dough crumbs evenly over the filling.
Bake the cake on the middle level of the oven for 35-40 minutes or until the crumble has acquired a Golden hue, and its filling begins to bubble.
Remove the finished crumble from the oven and cool completely.
If desired, serve it with vanilla sauce or vanilla ice cream.