Instructions
The plastic-wrapped doughnut tray line. Transfer Nutella to a plastic bag (or to a zip-lock bag and cut off the corner). Place Nutella in the center of each cavity to make the ring, then place it in the freezer until it is completely firm. Remove the Nutella rings from the pan, place them on a plate and put them back in the freezer until they are ready to assemble the doughnuts.
Preheat the oven to 350F. Brush the doughnut tray with melted butter, and set aside.
In a small bowl, stir together flour, baking powder and salt.
In another bowl, stir in the remaining melted butter (3 ½ tablespoons) and 2 ½ tablespoons of sugar. Add the cinnamon, vanilla, egg and milk and beat only to combine. Beat the flour mixture.
Transfer the mixture to a pastry bag (or zip-lock bag and cut off the corner). Fill the doughnut mold with half of the dough. Remove the Nutella rings from the freezer and place them on top. Cover the Nutella with the rest of the dough.
Bake for 13-15 minutes, or until golden and firm to the touch.
Place the doughnuts for 5 minutes in the mold and then invert on a rack.
In a bowl combine the cinnamon and sugar.
Melt 2 tablespoons of butter.
Brush each doughnut with the melted butter, then dip it in the sugar and cinnamon mixture.