Quarter new potatoes and place in a roasting pan. Add olive oil to coat, as well as rosemary and a few whole, unpeeled garlic cloves. Roast at 375°, tossing occasionally until cooked through and golden brown. Slip the garlic cloves from their skins and finely chop. Blanch peas -- frozen or fresh -- until crisp-tender and drain. Toss potatoes with the peas, garlic, any oil from the pan and a splash of cider vinegar.