In a large bowl, cream together the butter and sugar. Stir in flour and salt, mixing until just combined, making sure to scrape the sides and bottom of your bowl.
Cover and chill the dough in the refrigerator until it is firm enough to handle, about 15-30 minutes. You should be able to shape scoops of it into a ball without it being too sticky or cracking. If it is over-chilled and difficult to work with, leave it out on the counter for a few minutes.
Preheat the oven to 350°F and line a baking sheet with parchment paper.
Using a tablespoon, scoop dough and roll into balls (slightly under 1 ounce each). If desired, roll balls in sanding sugar until completely covered. Place dough cookie sheet, 2 inches apart.
Bake for 10 to 12 minutes. The cookies are done when their bottoms are lightly browned.
As soon as they come out of the oven, use a round teaspoon or the back of a wooden spoon to create shallow wells in the center of each cookie. Be careful not to press too hard or you can cause the cookies to crack. Set aside.