Preheat the oven to 200C/180C Fan/Gas 6. Lightly grease a 9 inch round cake tin.
Peel and dice the two apples to about 1cm dice.
In a large bowl, combine the melted butter, apple sauce, milk and eggs with a whisk until thoroughly mixed. Add in the sugar and mix again.
Add the flour, baking powder, baking soda and diced apples. Fold this together to form a cake batter. Pour this into the tin.
Make the crumble topping by combining all ingredients in a small bowl with a fork. Sprinkle the sand-like mixture over the cake. Bake for approx 35 minutes, until a skewer inserted comes out clean.
Let cool on a wire rack before making the glaze. Do this by combining the icing sugar and milk in a small bowl. Drizzle over the cake just before serving!