- 2 3/4 lb small red potatoes (about 1 1/2 inches in diameter)
- 3 tablespoons vegetable oil
- 2 teaspoons kosher salt
- 1/2 stick (1/4 cup) unsalted butter
- 2 teaspoons cider vinegar
- 1 teaspoon Dijon mustard
- Rounded 1/4 teaspoon cayenne, or to taste
- Put oven racks in upper and lower thirds of oven and preheat oven to 475°F. Put 2 large shallow baking pans (1 inch deep) in oven and preheat 10 minutes.
- Quarter potatoes, then toss with oil and 1 1/2 teaspoons kosher salt in a large bowl. Spread potatoes, cut sides down, in hot pans, then roast until undersides are golden, about 12 minutes. Turn potatoes so other cut sides are down, then switch position of pans and roast until potatoes are tender and undersides are golden, 12 to 15 minutes more.
- While potatoes roast, melt butter in a small saucepan and whisk in vinegar, mustard, cayenne, and remaining 1/2 teaspoon kosher salt.
- Toss hot potatoes with butter mixture in cleaned large bowl until coated.