Add to a heatproof dish and sprinkle over the sweetener or sugar
In another bowl add the caster sugar, butter and flour and mix with your fingers until it resembles breadcrumbs. Alternatively for speed, pulse in a food processor (but be careful not to overmix)
Sprinkle the crumble topping over the apples making sure they're all covered.
Sprinkle the demerera sugar over the top then bake in the oven for 35-40 minutes.
Serve with cream, custard or ice cream.
Recipe by Rainbowcrush.com at http://www.rainbowcrush.com/recipe-apple-crumble