1. In medium-size bowl, stir together flour and salt.
2. In second medium-size bowl, beat together sugar, butter, sour cream, egg yolk and vanilla until creamy and smooth, about 2 minutes. Stir in flour mixture until blended. Shape into disk; wrap in plastic wrap; refrigerate for several hours or overnight.
3. Heat oven to 350 degree F. Lightly coat 2 baking sheets with nonstick vegetable-oil cooking spray.
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 prepared 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; let cool completely. Makes 1-3/4 dozen cookies.
6. Using Royal Icing and stencils (see Note), paint holiday designs on cookies by holding stencil flat on top of cookie and, with clean 1/2-inch brush (used by artists), brushing colored icing through stencil onto cookie. Additional features may be painted freehand or piped on with a pastry bag.
1. In small bowl, beat together confectioners sugar, 2 to 3 tablespoons water and meringue powder until stiff and fluffy. Divide into 5 small bowls. Stir food coloring and a few drops water into 4 bowls; add just water to fifth bowl; icing should be thick and opaque but no longer hold a peak. Use a brush to paint the cookies.