In a bowl, combine flour and salt. Place sugar into a food processor and process until very fine. Add butter pieces and process until mixture is smooth and creamy. Add egg, lemon zest, and vanilla, and process until smooth. Add flour and pulse just until a dough forms.
Remove dough and cover with plastic wrap. Pat dough into a 1-inch-thick disk. Refrigerate for1-1/2 hours until firm.
Preheat oven to 350 degrees. Grease or line cookie sheets with parchment paper.
On a lightly floured surface, roll out dough to 1/8-inch thickness. With floured Christmas cookie cutters, cut out as many cookies as you can, keeping cutouts close. Sprinkle cookies with colored sugars or decorations. Transfer cookies to prepared sheets, allowing about 1 inch space between cookies. Gather scraps of dough and repeat process.
Bake in preheated oven for 10 to 12 minutes, or until lightly browned on edges. Remove from cookie sheets and cool completely on wire racks. Makes about 4 to 5 dozen depending on size of cutters you use. Enjoy!
*Note: These may also be baked plain, cooled, and then decorated with colored icings,sugars, etc.