Arrange a rack in the bottom third of the oven and heat to 425°F. Use 4 potatoes, scrubbed clean and patted dry. Alternatively, you can peel the skins off.

Cut parallel slits into each potato, stopping just before you cut through so that the slices stay connected at the bottom of the potato. Space the slices ⅛-inch to ¼-inch apart. You can rest the potato in a large serving spoon (or on 2 wooden chopsticks) and use that as a guide for when to stop slicing — slice straight down and when your knife hits the edge of the spoon, stop slicing.

Arrange the potatoes in a baking dish. Brush the potatoes all over with 2 tablespoons of olive oil or melted butter, including the bottoms. Sprinkle the potatoes generously with kosher salt and black pepper.

Bake the potatoes for 30 minutes. At this point, the layers will start separating. Remove the pan from the oven and brush the potatoes again with the remaining 2 tablespoons of olive oil or melted butter — you can nudge the layers apart if they're still sticking together. Make sure some of the fat drips down into the space between the slices.

Bake until the potatoes are crispy on the edges and easily pierced in the middles with a paring knife, 30 to 40 minutes. If you're adding any extras, stuff those into the slits and sprinkle over the top 5 to 10 minutes before the end of cooking. (Total baking time is 60 to 70 minutes for average potatoes; if your potatoes are on the small side or are larger, adjust cooking time accordingly.)

Serve immediately. These potatoes are best straight from the oven while the edges are at their crispiest.