Put the potatoes in a large pot with the cold water, which should cover them by about 1 inch (2.5 cm), and add 1 tsp of the salt.

Bring to a boil over high heat, then reduce to a steady simmer and cook until a knife slides into a chunk with no resistance, 15 to 20 minutes.

Drain well, then return the potatoes to the dry pot over low heat for 1 to 2 minutes, shaking the pot, until the steam thins and a floury film forms on the surface.

Mash with a hand masher or ricer until no lumps remain, adding 2 tbsp of the butter. Spread the mash on a rimmed baking sheet and cool until it stops steaming, 10 to 15 minutes.

Fold in the cheddar, egg, garlic powder, onion powder, black pepper, chives and the remaining ½ tsp salt with a spatula until just combined. Refrigerate for 30 minutes, until the mixture is firm enough to hold a shape, and do not taste it because it contains raw egg.

Heat the oven to 400°F (200°C) with a rack in the upper third, and line a baking sheet with parchment paper.

Melt the remaining 2 tbsp butter, then toss it with the panko in a shallow bowl until the crumbs look like damp sand.

Scoop the chilled mixture with a scant ¼-cup (60 g) measure and roll each portion into a ball, then roll it in the panko, pressing lightly so the crumbs cling. Set the puffs 1½ inches (4 cm) apart on the baking sheet to make 16.

Bake for 22 to 28 minutes, rotating the pan halfway through, until the shells are deep golden and a center reads 160°F (71°C).

Rest the puffs on the pan for 5 minutes so the cheese sets, then serve warm.