Use these crisp cookie cups to serve ice cream, sorbet, or fresh berries.
Beat together butter, sugar, and vanilla in a mixer on medium high until fluffy. Reduce speed to low, and beat in flour and salt until combined. Shape dough into a disk, and wrap in plastic wrap. Refrigerate until firm, at least 2 hours and up to overnight.
Roll out dough to 1/4-inch thickness on a lightly floured surface. Cut out six 4-inch rounds. Place rounds on alternating cups of an overturned standard 12-cup muffin tin, leaving empty cups in between. Gently press each round over the top of each muffin cup and down the sides about 1 inch, leaving a 1/2-inch border against the flat part of the muffin tin at the "bottom" of each overturned cup. Press together any cracks or holes. Refrigerate 30 minutes.
Meanwhile, preheat oven to 300 degrees. Bake until golden brown, about 24 minutes. Place muffin tins on wire racks, and let cool. Gently lift each cookie from the muffin tin by sliding a small spatula or knife under the edge.