Cream butter and cream cheese at room temperature with mixer until blended.

Add sugar, egg yolk, and vanilla.

Beat until blended.

Add flour a little at a time until blended. Dough will be thick and you may need to mix by hand instead of with a mixer.

Refrigerate overnight.

Roll thin, cut out with cookie cutters, and bake on a lightly greased cookie sheet for about 10 minutes at 350 degrees until just starting to brown.

Let cool before removing from cookie sheet.

Frost with frosting or glaze if desired.