In a large bowl, mix together ground almonds, chopped hazelnuts, cocoa powder and maple syrup.
Lightly grease a 23cm tin with a removable base and press the mixture in to the tin.
To make the chocolate filling, add the double cream and caster sugar to a pan and bring to the boil.
Remove from the heat and stir in the butter and chocolate until smooth. Leave to cool.
Gradually stir in the milk and pour the mixture into the nutty base.
Leave to set for 2-4 hours then serve with a dollop of thick cream.