Marshmallow Chocolate Toffee Crispy Cookies

Ingredients:   1/2 cup butter 3/4 cup packed brown sugar 1/2 cup sugar 1 large egg 1 teaspoon vanilla 1 cup flour 3/4 teaspoon salt 1/2 teaspoon baking soda 1 1/2 cups Rice Krispies cereal 2/3 cup mini marshmallows 1/4 cup mini semi-chocolate chips 1/4 cup...