12 chicken thighs, trimmed of excess skin and fat
1 C. thinly sliced onion
3 Tbls. plus 1 tsp. thyme leaves
2 chiles de arbol, thinly sliced on the diagonal
2 fresh bay leaves, thinly sliced; or 2 dried leaves, crumbled
3/4 C. dry vermouth
2 C. fresh breadcrumbs
5 Tbls. unsalted butter
2 Tbls. chopped flat-leaf parsley
1/2 C. finely diced shallots
1/2 C. Dijon mustard
1 extra-large egg
2 tsps. chopped tarragon
2 Tbls. extra-virgin olive oil
3/4 C. chicken stock
Braised leeks (recipe follows)
kosher salt and freshly ground pepper
Place the chicken thighs in a large bowl with the sliced onion, 2 Tbls. thyme, chiles, bay leaves, and 1/4 C. vermouth. Using your hands, toss to coat the chicken well. Cover and refrigerate at least 4 hours, preferably overnight.
Place the breadcrumbs in a medium bowl. Heat large saute pan over medium heat for 1 minute. Add 3 Tbls. butter, and cook until it's brown and smells nutty. Use a rubber spatula to scrape the brown butter over the breadcrumbs. Wait 1 minute, and then toss well with the parsley and 1 Tbls. thyme.
Preheat the oven to 375º.
Return the saute pan to medium heat for 1 minute. Swirl in the remaining tablespoons butter, and when it foams, add the shallots and remaining 1 teaspoon thyme. Saute about 2 minutes, until the shallots are translucent. Add the remaining 1/2 C. vermouth and reduce by half. Transfer to a bowl and let cool a few minutes. Whisk in the mustard, egg, chopped tarragon, and a pinch of black pepper.
Remove the chicken from the refrigerator 30 minutes before cooking, to bring it to room temperature. Discard the seasonings, and pat the chicken dry with paper towels. After 15 minutes, season the thighs well on both sides with salt and pepper.
Return the same saute pan to high heat for about 2 minutes. Swirl in the olive oil, and wait 1 minute. Place the chicken thighs in the pan, skin side down, and cook 8 to 10 minutes, until the skin is a deep golden brown. Turn the thighs over and cook a minute or two on the other side. Place the chicken on the braised leeks. Turn off the heat and discard the fat. Add the chicken stock to the pan, and scrape with a wooden spoon to release the crispy bits stuck to the bottom. Pour the chicken stock over the braised leeks.
Toss the chicken thighs in the bowl with the mustard mixture, slathering them completely, and then rearrange them over the braised leeks. Spoon any remaining mustard mixture over the chicken thighs. Top each thigh with breadcrumbs, patting with your hands to make sure they get nicely coated. (You want lots of mustard mixture and lots of breadcrumbs.) Bake about 40 minutes, until the chicken is just cooked through. To check for doneness, pierce the meat near the bone with a paring knife; when ready, the juices from the chicken will run clear.
Turn the over up to 475º and cook the chicken thighs another 10 minutes, until the breadcrumbs are golden brown.
Serve in the baking dish, or transfer to a large warm platter.