In a large mixing bowl, place the cold cubed butter, flour, icing sugar and hazelnut flour. Rub the ingredients in with your fingertips to prevent the butter from melting. Add the egg.
Mix softly until homogenous. Wrap in plastic film and place in the refrigerator for 1 hour.
Roll the pastry out into a 3-millimeter-thick circle. Line it in a pie plate removing the extra dough.
Melt the butter and apricot preserve, add the diced fruits, walnuts and orange zest. Then fill the pie.
Place in the refrigerator for 15 minutes then bake for 40 minutes at 180°C (th. 6 - 350°F).
