Put everything but the walnuts in a bowl and mix. Pinch the butter cubes with your fingers along with the flour until it becomes a homogeneous mix that looks like wet sand. For further reference watch the video lines above.
At the end add the walnuts and reserve. It's best to keep it in the fridge if it's a hot day.
Mix everything except the apples and reserve.
Peel, core and slice the apples to 2mm in thickness.
Mix the apples with the rest of the filling ingredients and lay in individual moulds or a large one. Press down gently to minimize the amount of air between them.
Put the crumble on top.
Take to a preheated oven at 180C for 40min or until golden ontop and bubbly.
Let rest for 15min before eating.