Potato, Italian Sausage, and Arugula Salad

Soak onion in cold water to cover 15 minutes.

Drain and pat dry.

Meanwhile, cover potatoes with salted cold water by 2 inches in a 3-quart heavy saucepan and simmer, uncovered, until just tender, 15 to 25 minutes.

Drain in a colander and cool slightly.

While potatoes are simmering, prick sausages once or twice with a fork, then cook in 1 tablespoon oil in a large heavy skillet over moderate heat, turning occasionally, until browned and cooked through, about 10 minutes.

Transfer to paper towels to drain. When sausages are cool enough to handle, cut diagonally into 1/2-inch pieces.

Whisk together vinegar and salt in a large bowl until salt is dissolved. When potatoes are just cool enough to handle (but still warm), peel and cut into 1-inch cubes, adding to vinegar as cut, and toss gently.

Add onion, sausages, roasted peppers, arugula, remaining 3 tablespoons oil, and salt and pepper to taste to potatoes and toss well.