• Preheat the oven to 375 degrees F. Place egg in a bowl and beat it with a spoon or whisk. Add ½ cup of the Nutella and beat until smooth. Stir in ½ cup of the flour. Slowly stir in remaining flour; batter will be thick and sticky.
• Drop 9 rounded tablespoons of batter onto a parchment lined cookie sheet, leaving about 2 inches of space.
• Bake for 10-12 minutes. Let cool for at least 10 minutes. Carefully cut cookies horizontally through the center; fill each with a rounded teaspoonful of Nutella. Chill cookies.

Non-Split Version

• Instead of dropping 9 large rounds, drop 16 to 18 smaller spoonfuls of dough onto the baking sheet. Bake for only 8 to 10 minutes (or just until done) and let cool. Use two cookies and create 8 or 9 sandwiches. Since they are not split, they'll be have a more rounded shape.