Put sugar, flour, and salt in the food processor and combine. Add in margarine, a little at a time. Then add in the cream cheese and vanilla and mix until dough begins to form large clumps.
Knead dough in the bowl by hand a few times until it forms a cohesive mass.
Shape into two disks and put these in the refrigerator until they are cold – about an hour or so.
Adjust oven rack to the middle position and heat oven to 375 °F. Roll out one disk of dough in between two sheets of parchment. (You don’t need to flour the surface, because parchment is nonstick!)
Roll out to 1/8 inch thickness and cut with cookie cutters.
Bake cookies for about 10 minutes, until light golden brown. Let cookies cool a few minutes on baking sheets before transferring to a wire rack.
If you don’t feel like rolling out cookies and icing them, it works nicely to just make these into little balls and roll in sugar (or colored sugar!). As the cookie flattens in the oven, it makes a nice snickerdoodle-type cookie.