Preheat the oven to 325°. In a medium bowl, combine the olive oil with the maple syrup, curry powder and cayenne and season with salt. Add the puffed grains and stir to coat. Spread in an even layer on a parchment paper–lined baking sheet and bake, stirring twice, until lightly browned, about 20 minutes; the mix will crisp as it cools. Break up any big clumps.
Halve the potatoes lengthwise and scoop out the flesh, leaving a thin wall of flesh on 4 of the halves. (Discard the remaining 4 empty shells.) Mash the potato flesh with the butter and season with salt. Spoon the mixture back into the shells and bake until hot, about 15 minutes. Transfer the potatoes to plates and sprinkle with some of the puffed grains. Serve right away, passing extra puffed grains at the table.