Add the butter, milk, salt and flour to a bowl, and mix well using your hands until you have a smooth dough that is not sticky. Add the grated parmesan and mix again.
Line a large baking tin with nonstick paper. Take walnut-sized pieces of dough and make into cookies. Place them on the baking tin, somewhat apart from each other.
Bake in a preheated oven at 180° C for 15' and remove from the oven. Leave the biscuits to cool very well before serving, because they might crumble when hot.