1Grease 13x9-inch (3-quart) glass baking dish or pan with shortening, or spray with cooking spray.
2In 6- to 8-quart Dutch oven, melt butter over medium heat. Add marshmallows and salt; cook 3 to 5 minutes, stirring occasionally, until marshmallows are completely melted and bubbly.
3Remove from heat. Gently stir in both cereals until completely mixed and melted marshmallows are evenly distributed.
4Using large spoon or rubber spatula, press mixture in baking dish. Cool 15 minutes. Cut into 6 rows by 4 rows.