10 ounces pearl onions
3 tablespoons unsalted butter
1 medium leek, cut into 1/2-inch-thick slices (white and pale green parts only)
2 tablespoons finely chopped garlic
3 medium carrots, large dice
2 medium celery stalks, medium dice
2 teaspoons coarsely chopped fresh thyme leaves
5 tablespoons all-purpose flour
1/2 cup dry white wine
2 cups low-sodium chicken broth
2 pounds cooked turkey meat, cut into large pieces
5 cups mashed potatoes