Preheat oven to 325 degrees F (165 degrees C). Lightly grease cookie sheets.
In a large bowl, cream together butter, cream cheese, and sugar until light and fluffy. Beat in egg yolk and vanilla. Stir in flour until well blended. Drop dough by spoonfuls or use a cookie press to place onto prepared cookie sheets. If using floral cookie press design, make an indentation in the center with a thimble, fill with preserves, or press candy into center.
Bake for 15 minutes in preheated oven. Cookies should be pale.