Line an 8-inch square pan with aluminum foil; set aside.
Combine sugar, marshmallow cream, evaporated milk, butter, and salt together in a large saucepan over medium heat; bring to a full boil and cook for 5 minutes, stirring constantly.
Remove from heat and add milk chocolate chips and semisweet chocolate chips; stir until chocolate is melted and mixture is smooth. Stir in nuts and vanilla. Pour into prepared pan; chill in refrigerator for 2 hours, or until firm.