Preheat the oven to 350 degrees . In a 9-by-13-inch baking pan, mix the salt and oregano; spread in an even layer. Nestle the potatoes in the salt, 1 or 2 inches apart.
Bake until the potatoes are tender when pierced with the tip of a knife, about 1 1/2 hours. Scrape off the salt and arrange the potatoes on a platter. Slice open, top with butter and season with salt and pepper.