
5 tablespoons salted butter, plus additional softened butter for greasing
1 (16-ounce) package mini marshmallows (10 cups)
7½ cups crispy rice cereal
½ cup rainbow nonpareils
1½ cups white baking chips
2 tablespoons neutral-flavor oil, such as avocado, vegetable or canola oil
Rainbow nonpareils, for garnish