Prepare the béchamel (go here for the recipe)
Put the potatoes in a saucepan with cold water, bring to a boil and cook for 40 minutes. Then drain, peel the potatoes and pass them in the potato masher to obtain a puree that you will collect in a bowl.
Now add the speck cut into small pieces, the béchamel, the Parmesan, the yolk and the salt and mix everything together.
Roll out the puff pastry on a flat surface, cut out circles and line the buttered tart molds with them. Prick the base of the tartlets with the prongs of a fork.
Pour the potato mixture onto the pastry. With a small wheel we extract strips from the dough puff pastry and put them on our tartlets. Brush the surface of the threshold with a beaten egg and bake in a preheated oven at 200 ° for 15/20 minutes.
Leave to cool and then serve.