In a small mixing bowl, beat butter with electric mixer at medium speed for 30 seconds. Beat in powdered sugar until smooth. Beat in egg yolk until well combined. Add flour; beat on low speed until well combined. If necessary, use hands to knead dough and shape into a ball. If necessary, cover and chill until dough is easy to handle.
On well-floured surface, roll dough to 1/8-inch thickness. With a 2-inch-diameter cutter, cut out cookies. Place 1 inch apart on ungreased cookie sheet.
Bake in a 375 degree F oven for 5 to 7 minutes or until golden brown. Cool on a wire rack. Makes about 20 cookies.