4large Yukon Gold or Idaho potatoes, about 10 ounces each,scrubbed
6tablespoonsbutterat room temperature
1tablespoonchopped fresh rosemary
Salt to taste
Heat the oven to 400 degrees.
Spread about a ½-inch deep layer of salt on the bottom of an 8 x 12-inch heavy casserole or baking dish. Nestle the potatoes in the salt, then pour the remaining salt evenly all around the potatoes (a portion of their tops will be uncovered).
Bake for one hour. If a skewer easily pierces through the potatoes, they're done. If not, continue baking up to an additional 30 minutes, depending on the size of your potatoes.
In a small bowl, mash the butter with the rosemary.
Make a slit down the center of each potato and smoosh the tops to open. Divide the butter over the potato flesh. Sprinkle with salt and serve.
You can reuse the salt after baking the potatoes — strain through a colander to remove clumps and particles.