Mix the butter with the sugar until the sugar is well blended, add the vanilla and the Nutella to it.
Add the orange zest, the egg an the water. Sift the cornstarch together with the envelope of baking powder and the flour.
Form the pastry getting all togehter and let it rest for 15 minutes on the fridge.
Roll the pastry out until 4 mm thick and cut circles from it from 5 cm in diameter.
Lay the circles on a dish and place them in the freezer until they become hard.
Preheat the oven at 190 degrees celcius.
Lay the cookies on a baking dish (covered with baking paper) and bake them only 5 minutes.
Fill the half of the cookies with the dulce de leche and cover them with the other half of the cookies.
Then give them a cover with melted chocolate.