Preheat oven to 500°F

Parboil the sausages in water in a covered pan for about 8 to 10 minutes.

Melt the butter in a small flameproof roasting pan /oval baking dish.

With tongs put the sausage in the pan of grapes, press them down into grapes so they will not brown too fast.

Roast in the oven until grapes are soft and the sausage has browned, turning to brown every few minutes (in about 20 to 30 minutes it should be done.)

With a slotted spoon transfer the sausage and grapes to a heated platter.

Place the roasting pan on top of the stove and on medium-high heat, add the balsamic vinegar - scrape up any brown bits on the bottom of pan, and cook until the vinegar and juices are reduced until thick and syrupy. If it doesn't get thick add some corn starch with water. Add the sausages and grapes in the syrup. Put on top of polenta or mashed potatoes.