Sauté shallot in hot oil in a medium skillet over medium heat 2 minutes or until soft; add garlic, and sauté 1 minute. Stir in wine, mustard, and sugar; bring to a boil. Cook, stirring constantly, 3 minutes or until mixture has thickened and is reduced by about half. Remove from heat, and whisk in sour cream, salt, and pepper. Serve immediately.