In a medium bowl beat for approximately 2 minutes Nutella and egg.
Add sifted flour and mix with a spatula or wooden spoon. Form into a ball, wrap in plastic and refrigerate for 20-30 minutes.
Pre-heat oven to 350°F (180°C), line a cookie sheet with parchment paper.
Remove dough from fridge and roll into 10-12 balls, with finger or bottom of wooden spoon press down the center of each ball, making a deep well in the middle - deep but not too wide.
Fill a pastry bag with Nutella.
Depending on how you like your cookie (or do half and half and then decide), fill the unbaked cookies (or leave unfilled) with Nutella and Bake for approximately 10-15 minutes, cookies will be a little soft but will firm up while cooling. Cool completely before filling unfilled cookies with Nutella. Sprinkle with chopped nuts if desired. Enjoy!
**dough will be soft and hold together, add flour gradually.***Make sure the Nutella is nice and soft and not too hard.