Using a food processor or a dough cutter (or a fork), combine unsalted butter, flour, sugar and salt until loosely combined
Slowly add the cold water and watch until it begins to clump together. Once this happens stop pouring water and stop the machine or mixing.
Roll the dough into a ball and then into a thick disk shape. Wrap in plastic wrap and place in the refrigerator for at least 30 minutes or up to a day.
Roll out on a pastry sheet or counter top using a dusting of flour and sugar. Roll out until the proper size has been achieved for your tart pan.
Rub unsalted butter over the pan's sides and bottom to prevent the tart from sticking.
Place the dough in the pan. Gently press the dough into the bottom corners and then using a rolling pin, roll it across the top of the pan to create a clean, even edge