Heat oven to 180C. Grease and line an 8 or 9 inch pan with parchment paper.
Cream the butter and brown sugar in large bowl, 2-3 minutes on medium speed until light and fluffy.
Add the eggs one at a time until mixed, then vanilla.
Add the flour, baking powder, salt and cinnamon and fold until just combined, then fold in the apple cubes. Batter will be thick! Spread into prepared pan.
Combine all the crumble ingredients in a small bowl, pinching together with fingertips until small crumbs form, then scatter evenly onto cake surface.
Bake for 40-45 minutes until toothpick comes out clean.