Preheat oven to 180ºC . In a large bowl, beat butter and sugar until smooth. Beat in the egg and vanilla extract. Set aside. In a small bowl, combine flour, baking soda, and salt and mix together well. Add flour mixture to the batter and mix until well blended. Stir in the Rice Crispies and chocolate chips. Drop by level tablespoonfuls onto greased cookie sheet. Bake about dozen minutes or until light brown. Remove cookies to wire rack to cool. These freeze well. Walt MM