Place sugars, salt, milk, and butter in saucepan, bring to a full boil over medium heat, Stirring constantly for 5 minutes. Remove from heat, Add marshmallow cream and vanilla, Stir until smooth.Take 2 cups of the hot mixture and add butterscotch chip and half the walnuts, stir til chips are melted and mixture is smooth. To remaining mixture add chocolate chips and the other half of the walnuts til chips are melted and mixture is smooth. Pour chocolate mixture into well greased 9 inch square pan, then add butterscotch mixture. Chill until firm. Cut in squares.