Step 1

Put the racks in the top and center positions and preheat the oven to 400 degrees F.

Step 2

Heat the butter and olive oil in a large cast-iron or ovenproof skillet over medium-high heat. Add the potatoes in a single layer, then sprinkle with a good pinch of salt and several grinds of black pepper. Cook until the first side is golden brown, about 4 minutes.

Step 3

Meanwhile, whisk the broth, maple syrup, pepper flakes and 1/4 teaspoon salt in a small liquid measuring cup until combined. Flip the potatoes carefully with tongs, then pour the broth mixture over and top with the fresh thyme.

Step 4

Transfer the skillet to the oven and bake on the center rack until the potatoes are very tender and the broth mixture has reduced slightly, 20 to 25 minutes.

Step 5

Remove the skillet from the oven and preheat the broiler to high. Top each piece of potato with a marshmallow half, cut-side down. Broil on the top rack until the marshmallows are puffed and lightly toasted, about 1 minute. Watch closely to prevent burning.