How to Make It
Preheat the oven to 350° and line a large rimmed baking sheet with foil. Prick each potato all over with a fork and transfer to the baking sheet. Bake the potatoes until tender, about 1 hour; turn the potatoes over halfway through baking. Let cool slightly.
Meanwhile, lightly coat a large rimmed baking sheet and 2 large spoons with nonstick cooking spray. Lightly coat a large heatproof bowl with nonstick cooking spray and put the Rice Krispies in it. In a small bowl, mix the baking soda with the 1/4 teaspoon of salt and 1/8 teaspoon of cayenne. In a medium saucepan, combine the sugar with 1/2 tablespoon of the butter
and 1/4 cup of water and bring to a boil, stirring until the sugar dissolves. Boil over moderately high heat, swirling the pan occasionally, until a golden caramel forms, about 7 minutes. Remove from the heat and stir in the baking soda mixture; the caramel will foam. Immediately drizzle all of the hot caramel over the cereal and, using the 2 greased spoons, quickly toss to coat. Spread the topping on the prepared baking sheet in an even layer and let cool completely, then break into pieces.
Scoop the sweet-potato flesh into a food processor. Add the remaining 6 tablespoons of butter and the cream, orange zest and a generous pinch of cayenne and puree until smooth. Season with salt and black pepper. Transfer the sweet potatoes to a serving bowl and dollop with additional butter. Serve, passing the crispy rice topping at the table.