Cut butter into small cubes.
Combine flour, sugar and salt in a large bowl.
Work butter into the flour mixture with a pastry cutter.
Whisk together one egg and milk and add to the flour mixture.
Knead until ball forms.
Turn dough out on to floured surface and knead for 1 minute.
Refrigerate dough for 30 minutes.
Preheat oven to 350.
Divide in half.
On floured surface, roll out dough into a 9" × 12” rectangle.
Cut into 9 rectangles.
Repeat with other piece of dough.
Make an eggwash by beating the remaining egg and brush over entire surface of first 9 rectangles.
Place a tablespoon of Nutella on top of each egg washed rectangle and spread. Be sure to leave 1/2" bare around edges.
Place a rectangle on top of filling and press with fingertips to seal around edges.
Use the tines of a fork to seal all around.
Poke top with fork to allow steam to vent.
Place on parchment lined baking sheet and bake for 25 minutes or until lightly browned.
Cool on wire rack.