Heat 1 tablespoon of the olive oil in a medium saucepan. Add the shallots and cook until softened, 3 to 5 minutes. Add the wine and boil until reduced by half, about 10 minutes. Add the chicken stock and boil until reduced by one-third.
Meanwhile, in a medium enameled cast-iron casserole, heat the remaining 1 tablespoon of olive oil. Add the sausages and cook over moderately high heat until browned, about 3 minutes per side. Add the water and bring to a boil. Reduce the heat to low, cover and simmer until the sausages are cooked through, about 20 minutes.
Bring the wine sauce to a boil. Remove from the heat and whisk in the butter, 1 piece at a time. Season with salt and pepper. Cut the sausages into 2-inch pieces and arrange an assortment on each plate. Top with the sauce and serve with the Potato Gratin.