Start by sifting the flour and forming a volcano shape on your countertop.
Add the butter, cut into pieces, in the middle of the crater. Work the ingredients together very fast until they are crumbling together (see notes).
Add the sugar, the egg yolks, the vanilla and the salt and continue working together with all the ingredients until they are perfectly combined. Place the dough in the refrigerator and let it rest for 1 hour.
Just before taking out the dough from the refrigerator, preheat the oven at 320°F (160°C).
Roll out the dough with a rolling pin to a ¼ inch thickness and then cut as many forms as you can using heart-shaped cookie stamps.
On half of the cookies you get, make a smaller heart imprint with a smaller heart-shaped cookie cutter. This will give you a cookie with a heart hole.
Cover a baking sheet with parchment paper, place the cookies on top and cook them in the oven for 8-10 minutes until golden (see notes).
Let them cool down on baking rack. Once cold, cover the cookies with a heart-hole with icing sugar and spread some Nutella on the other cookies.
Place the cookie with a hole on the top of the whole cookies, so that you will have 2 heart-shaped cookies that have a heart filled with Nutella. Your cookies are ready! MANGIA and ENJOY IT!