Preheat the oven to 170° C w/ fan.
Trim & cut the rhubarb in thin slices.
Hull & trim the strawberries; cut them in halves or quarters.
Mix the fruit in the casserole w/ sugar, lemon juice & cornstarch.
Mix flour, cocoa, baking powder & salt.
Add sugar & cubed cold butter & knead the mess w/ your hands until well mixed.
Add the liquid whipping cream & fold in w/ a spoon.
Pour the batter over the fruit mix & distribute the batter evenly. You don't need to cover all of the fruit.
Bake it in the preheated oven for about 40 min.
It's ready for serving after the oven session - just let it cool for about 10 - 15 min.