Beat, the butter along with the sugar, until the texture becomes fluffy.
Add melted and chilled chocolate, vanilla and yolk, mix until homogenized.
Sifer flour, cocoa powder, mix again and form a bile.
Give the dough to the refrigerator for 30 minutes.
Form the balls, transfer to a baking tray, lined with baking paper, make a depth in the middle of each ball, bake for 12-14 minutes, temperature 160 C.
Cool completely.
Fill each depth with boiled condensed milk, sprinkle with salt.
Enjoy!
