In a large bowl, cream shortening and sugars until light and fluffy. Add eggs, one at a time, beating well after each addition. Beat in vanilla. Combine the flour, baking soda and salt; gradually add to creamed mixture and mix well. Stir in the marshmallows, chips and walnuts.
Spread into a greased 13-in. x 9-in. baking pan. Bake at 350° for 25-30 minutes or until golden brown. Cool on a wire rack. Cut into bars.