3/4 pound small red-skinned potatoes, halved, or quartered if large
Kosher salt
2 sprigs fresh rosemary, plus 1 tablespoon leaves
1 clove garlic, smashed
Pinch of red pepper flakes
Juice of 2 lemons (squeezed halves reserved)
2 tablespoons extra-virgin olive oil
4 skin-on, bone-in chicken breasts (6 to 8 ounces each)
10 ounces cremini mushrooms, halved