Preheat oven to 350 degrees.
In a large bowl, combine margarine, sugar, salt, egg and vanilla, using an electric mixer blend until smooth. Mix in flour.
Drop by tablespoons onto greased cookie sheet. Press a thumbprint into the center of each ball, about ½-inch deep. Fill each indentation with about 1 tsp jam. Bake for 9 minutes.
Makes about two dozen.