Step 1

Place the potatoes on a microwave-safe plate in an even layer, then microwave on high until knife-tender, flipping each halfway through, 5 to 6 minutes. Set aside to cool slightly.

Step 2

Cut each potato in half crosswise. Use a 1/4 teaspoon measuring spoon to scoop out the potato, leaving a thin border around the edge. Transfer the scooped-out potato to a medium bowl, then cover and reserve.

Step 3

Meanwhile, fill a large heavy-bottom pot or Dutch oven with 2 inches of canola oil and attach a deep-fry thermometer to the pot. Heat the oil to 350 degrees F over medium-high heat. Line a rimmed baking sheet with a couple paper towels; set aside.

Step 4

Whisk the potato starch and 1/3 cup water in a medium bowl until smooth. Dip the potato shells into the potato-starch slurry, letting any excess drip back into the bowl, then carefully lower into the hot oil. Cook, in batches, until well browned and crispy, about 4 minutes per batch. Remove from the hot oil with a slotted spoon and place cut-side up on the prepared baking sheet. Season with salt and then flip over cut-side down to drain.

Step 5

Add the butter to the reserved scoop-out potato and reheat in the microwave until warm, stirring halfway through, about 3 minutes. Use a fork or potato masher to mash the potato until almost smooth, then stir in the sour cream, Cheddar, scallions, 1/2 teaspoon salt and several grinds of black pepper until combined.

Step 6

Using the 1/4 teaspoon measuring spoon, spoon the filling into the crispy potato skin scoops. Transfer to a serving platter and sprinkle with a pinch of cayenne.