In a large bowl*, gently whisk together flour, sugar and baking powder, create a well in the middle, add the slightly beaten egg and yolk and the room temperature butter cut into pieces. Mix together, at this point turn mixture onto a slightly floured surface and work the mixture to form a soft dough (if dough is very dry then add an extra tablespoon of soft butter).
Wrap the dough in plastic and refrigerate for 30 minutes. Remove from fridge and knead the dough a couple of times to soften it up again on a lightly floured surface. Roll out to 1/8" thickness.
Pre-heat oven to 350F (180C), grease and flour an 8 or 9 inch- (20 - 22 cm) pie dish.
Transfer to prepared pie plate, I used a 8" pie dish (20 cm). Trim the dish of any extra dough. Prick the dough with the tongs of a fork, then spread the pastry shell with the Nutella. With the extra dough make strips to create a lattice finish. Brush the top lightly with milk and bake in pre heated oven at 350° (180°) for 25-30 minutes or until golden. Let cool then slice, enjoy!
*I also make the dough using a food processor, whisk the ingredients together in the food processor cup, then add the egg, yolk and butter and pulse until almost combined, moved to a lightly floured surface and knead gently to completely combine. Wrap and refrigerate.With any extra dough, I made squares and I placed 1 teaspoon of jam in the middle, folded it over, pinched the sides closed and baked in the oven for about 20 minutes at 350° (180°)).