Peel, core and cut the apples and pears into 2cm chunks.
Mix together the sugar, corn flour, cinnamon and nutmeg until well combined. Mix in the apples and pears. Stir together the melted butter and vanilla extract and pour this over the combined apples and pears, toss together well. Transfer the prepared apples and pears into an ungreased 9x13 inch baking dish and set aside.
Preheat oven to 180°C. In a medium size bowl, mix together the flour, baking powder, brown sugar, cinnamon, rolled oats, coconut and roughly chopped walnuts. Ensure that any lumps in the brown sugar are broken up. Add the cubes of cold butter and with your fingertips pinch together the dry mixture with the butter until a loose dough is formed.
Press small handfuls of the dough into balls. Break off small pieces of the dough, about the size of the top of your thumb, and scatter them evenly all over the surface of the prepared fruit layer. Do not press them down at all. This is key to getting a crispy crumble.
Bake in the oven for about 45 minutes. The fruit layer should be bubbling, and the surface of the crumble should be an even golden brown colour. Serve warm or cold with cream or your favourite ice-cream.