1 large onion, thinly sliced
2 tablespoons unsalted butter
4 pounds sauerkraut, rinsed and drained
2 Gala, Fuji, or Red Delicious apples, thinly sliced
1 cup dry white wine
1 to 2 tablespoons packed dark brown sugar
Cook onion in butter in a 4-to 5-quart heavy pot over medium-high heat, stirring occasionally, until golden, about 6 minutes. Stir in sauerkraut, apples, and wine and bring to a simmer.
Cover pot and reduce heat, then simmer, stirring occasionally, until sauerkraut is very tender, about 2 hours.
Stir in 1 tablespoon brown sugar and 1/2 teaspoon each of salt and pepper. Add more brown sugar, salt, and pepper to taste.