Peel, core and cut the apples into thick wedges.

Mix together the sugar, corn starch, cinnamon and nutmeg until well combined then toss together with the apples.

Stir together the melted butter and vanilla extract. Pour over the apples and once again, toss together well.

Transfer the prepared apples to an ungreased 8x8 glass baking dish or one of similar size. I sometimes use a deep dish pie pan.

Preheat oven to 350 degrees F.

Mix together the flour, baking powder, brown sugar and rolled oats. Rub this together with your hands to break up any lumps in the brown sugar.

Add the cubes of cold butter and start pinching them together with your fingertips and incorporating them into the dry ingredients until the mixture forms a a ball like cookie dough.

Press small handfuls of the dough into balls, then 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 apple layer. Do not press them down at all. They will settle naturally as the crumble bakes. This is key to getting a crispy crumble.

Bake in the preheated oven for about 45 minutes. The apple layer should be bubbling and the surface of the crumble should be an even medium golden brown. If you are using a shallower, slightly larger baking pan like a 9x9, watch it closely, the crumble may be done in 5 or 10 minutes less time.