In the bowl of a stand mixer, beat butter and cream cheese.
Add in sugar, salt egg and vanilla. Beat until creamy.
Gradually add in flour, 1/2 cup at a time, while mixer is on low speed.
Transfer dough to a zip-top bag or a plastic container with a tight-fitting lid.
Refrigerate 2 hours, or overnight.
Remove dough from refrigerator, open bag or unseal container lid, and allow to warm on counter until easily pliable - about an hour, but this depends on how warm your kitchen is at the time.
Divide the dough in half.
Roll out half the dough on a well floured surface, using a well floured rolling pin, until about 1/8 inch thick - on the thicker side is better than too thin!
Cut out cookies using various cookie cutters.
Place on ungreased cookie sheets (non stick baking mats work great) and decorate with sugar or sprinkles if desired (leave the frosting or gel decorations for after baking).
Bake at 375 degrees for 7 - 9 minutes, or until just slightly brown on the edges.
Transfer to cooking racks and decorate with icing when completely cool.