Step 1

Preheat oven to 400F.

Step 2

Toss onions, leek, garlic, 2 tablespoons oil, thyme and salt in a large bowl until the vegetables are well coated. Spread the mixture in a nonreactive 9-by-13-inch baking dish (see Tip). Place the chicken pieces on the vegetables. Bake for 10 minutes.

Step 3

Whisk mustard, shallot, rosemary, soy sauce and pepper in a small bowl; gradually whisk in the remaining 1 tablespoon oil.

Step 4

After 10 minutes, brush the chicken with the mustard glaze. Continue baking until an instant-read thermometer inserted into the thickest part of a leg or breast (without touching bone) registers 165 degrees F, 30 to 45 minutes more. Serve the chicken with the vegetables.