Preheat oven to 350 degrees F (175 degrees C). Grease a 9 inch tart pan.
In a medium bowl, cream together the butter and sugar until light and fluffy. Beat in the egg and vanilla. Combine the flour and salt; stir into the creamed mixture.
Press dough into prepared tart pan. Bake for 15 to 20 minutes in preheated oven, or until lightly browned.