In the same pan, add the onions and garlic over high heat, stirring with a wooden spoon to dislodge browned bits. You may also add 1 tablespoon or 2 of water to keep the vegetables from sticking. Cook vegetables 5 minutes, until tender and golden brown. Return the sausages to the pan and cook another 3 minutes. Add the grapes and continue to cook over high heat until the grapes burst. Their liquids and pulp will mingle with the pan juices from the onions and garlic. Season with salt and pepper to taste. Drizzle with Saba and serve immediately.