1. Stir together flour and salt in a medium-size bowl.
2. Beat together sugar, butter, sour cream, egg yolk and vanilla in bowl until creamy and smooth, about 2 minutes. Stir in flour mixture. Shape into disk; wrap in plastic wrap; refrigerate several hours or overnight.
3. Heat oven to 350 degrees F. Lightly grease 2 baking sheets.
4. Roll out dough on lightly floured surface to 3/8-inch thickness. Cut into rounds with 3-inch scalloped cookie cutter. Reroll scraps; cut out. Place on greased baking sheets, spacing 1-1/2 inches apart.
5. Bake in 350 degree F oven 10 to 12 minutes or until lightly browned at edges. Remove cookies to wire rack to cool completely.
6. Using Royal Icing and stencils, paint holiday designs on cookies by holding stencil flat on top of cookie and, with clean 1/2-inch artists brush, brushing colored icing through stencil onto cookie. Additional features may be painted freehand or piped on with a pastry bag. Makes 1-3/4 dozen cookies.
1. Beat together confectioners sugar, water, and meringue powder in small bowl until stiff and fluffy. Divide into 5 small bowls. Stir food coloring and a few drops water into 4 dishes; add just water to fifth bowl; icing should be thick and opaque but no longer hold a peak. Use to paint the cookies.