Roasted Italian Sausage, Peppers, and Onions

sweet or hot Italian sausages (or a combination of the two), cut crosswise into thirds

small red potatoes, cut into large chunks

large (about 1 pound) onion, cut into 12 wedges

red and/or yellow peppers, cut lengthwise into 8 pieces

few sprigs rosemary

About 1 tablespoon olive oil

heaping teaspoon kosher salt

Freshly cracked black pepper