Heat the oven to 200`c. start by chopping 100g of the toasted hazelnuts and place into a large bowl with ½ tsp cinnamon, flour, 225g butter, 100g sugar in a bowl and rub together until the mixture binds together. Press the dough into a 9 inch square tin lined with the base and sides lined with baking paper. Bake for 35 minutes till firm. Next, place the remaining ½ tsp cinnamon, 45g butter, 50g caster sugar, maple syrup and the light brown sugar and boil for 5 minutes. Add in the remaining 300g whole toasted hazelnuts and mix well to coat. Pour this mixture over the baked biscuit base, spread out and bake in the oven at 165`c for roughly 15 minutes or until the caramel has begun to set. Allow to cool down completely before cutting into squares.