1. Beat butter at medium speed with an electric mixer until creamy. Add sugar gradually, beating well. Add eggs and vanilla; beat well.
2. Combine flour and salt in a large bowl; beat into butter mixture gradually. Divide dough into 4 pieces, and flatten into disks. Wrap in plastic wrap; chill 1 hour.
3. Preheat oven to 350°. Line 2 baking sheets with parchment paper.
4. Roll each portion of dough to 1/4-inch thickness on a lightly floured surface. Cut out with 3- or 4-inch cookie cutters. Place on prepared baking sheets.
5. Bake 8 to 10 minutes or until cookies are lightly browned around edges. Let cool 3 minutes on baking sheets; transfer to wire racks to cool completely.
6. Pipe cookies with Royal Icing; garnish, if desired.