Cream butter and xylitol, add egg and mix. Add dry ingredients and mix together. Set the berries aside.
Press two-thirds of the crust into the bottom of a 9X13 pan lined with parchment paper or oiled. Bake at 350° for 15-20 minutes until just starting to brown.
To make a sauce whisk together Xylitol, arrowroot and nutmeg in small bowl. In a small saucepan, combine water and dry mixture with a whisk. Cook over medium heat, stirring constantly, until sauce thickens.
Pour over fruit, which has been placed on top of the cooked crust. Crumble remaining hazelnut crust topping over the mixture. Bake for 25-30 minutes
