Put the whole scrubbed sweet potatoes in a large pot, cover with cold water, and add 2 tablespoons kosher salt. Bring to a boil and simmer 18 to 22 minutes, until a knife slides into the center with no resistance.

Drain and leave the potatoes in the colander for 10 minutes so the residual heat steams off surface moisture, then pat each one dry.

While they drain, set the oven to 425F with an oiled rimmed sheet pan inside so the pan preheats with the oven.

Set the potatoes on the hot oiled pan with space around each one. Press straight down on each with the flat bottom of a glass until it is about ½ inch thick and the sides have cracked and torn. Do not press flatter than that.

Drizzle or brush the tops with the olive oil, then season with the kosher salt and black pepper.

Roast 25 to 30 minutes without turning them, until the torn edges are deep brown and crisp and the bottoms have set into a crust.

Melt the butter, take it off the heat, and stir in the minced garlic, thyme, and chili flakes.

Move the potatoes to a serving plate and spoon the garlic herb butter over them. Serve within about 15 minutes, and do not stack them.