French Onion Chicken

Bahan-bahan (4 porsi)

• 1 jumbo yellow onion (thinly sliced (about 12 ounces or 3 1/2 cups))
• 8 ounces good-quality sourdough bread (whole grain if possible, cut into 1 1/2-inch cubes (about 3 1/2 heaped cups))
• 8 cloves garlic (peeled and left whole)
• 2 tablespoons unsalted butter
• 2 tablespoons extra-virgin olive oil
• 1 tablespoon Dijon mustard
• 2 teaspoons kosher salt (divided)
• 2 1/4 pounds bone-in, skin-on chicken breasts
• 1/2 teaspoon ground black pepper
• 1 1/2 tablespoons chopped fresh thyme