Bring a pot of salted water to boil. Add potatoes and cook until fork tender. (I test potatoes by sliding in a knife -- if the potato clings to the knife, they're not done.) Drain potatoes. Heat oven to 450 degrees.
Drizzle a roasting pan or baking sheet with olive oil. Place potatoes on the sheet in a single layer, leaving space between each one. With a potato masher, press down on each potato until it slightly mashes open. Rotate the potato masher 90 degrees and mash again. Brush the tops of each crushed potato generously with more olive oil.
Sprinkle the potatoes with kosher salt (or flaky sea salt), black pepper and chopped fresh rosemary (or thyme or chives).
Bake for 20 to 25 minutes until the craggy edges are browned.
Serves 4 (although the amounts are very adaptable.)
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