In a large bowl or the bowl of a stand mixer, beat together the butter and cream cheese until well blended and smooth. Add the sugar, vanilla extract, and egg yolks, and mix until combined.

Add the flour and salt, and mix to form a soft dough. Shape the dough into a ball and wrap in plastic wrap. Refrigerate for at least 2 hours, or until firm.

Preheat the oven to 350F. Line 3 baking sheets with parchment or silicone baking sheets. Roll the dough out on a lightly floured surface to 1/4 inch thick. Cut the dough into desired shapes with cookie cutters, and place one inch apart on prepared baking sheets. Chill for 15 minutes to firm up the butter.

Bake for 10 to 12 minutes, until light golden brown around the edges. Bake time will vary with the size and thickness of the cookies. Allow to cool completely before frosting or decorating.