Start by putting 2 cups frozen berries in a pot and place on medium heat. Put the corn flour in a cup and pour some hot water to dissolve it - pour the corn flour liquid into the pot of berries. Cook over low heat for 15 mins.
While the berries are cooking start the crumble layer. Mix all these ingredients in a bowl and mix using a spoon.
In a baking tray place a layer of the crumble, top it off with the berry mixture & finish off by adding another layer of crumble ( sandwich the berry layer with the crumble layer)