Preheat oven to 325°F. Mix flour and salt in large bowl. Set aside. Beat butter and sugar in large bowl with electric mixer on medium speed until light and fluffy. Add egg and vanilla; mix well. Gradually beat in flour mixture on low speed until well mixed.
Roll dough on generously floured surface to 1/4-inch thickness. Cut out circles with 3-inch round cookie cutter. Place a standard muffin pan, upside down, on work surface. Press a dough circle around each ungreased muffin cup. (If using a nonstick muffin pan, see tips for best results.)
Bake 10 minutes or until edges are just beginning to turn golden brown. Cool on muffin pans 5 minutes or until cool enough to remove. Remove to wire racks; cool completely. Fill as desired.