1. Combine first 4 ingredients with 2 tablespoons thyme and 1/4 cup vermouth in a large bowl, tossing to coat. Cover and refrigerate at least 4 hours or overnight.
2. Prepare Braised Leeks, set aside.
3. Melt 3 tablespoons butter in a medium saucepan over medium-low heat; cook 3 minutes or until golden brown. Stir in breadcrumbs, parsley, and 1 tablespoon thyme. Set aside.
4. Melt remaining 2 tablespoons butter in a skillet over medium heat; add shallots and remaining 1 teaspoon thyme. Sauté 2 minutes or until shallots are translucent. Stir in remaining 1/2 cup vermouth. Simmer over medium-high heat until reduced by half. Transfer to a bowl; cool 10 minutes. Whisk in mustard and next 3 ingredients; set aside.
5. Remove chicken from marinade, discarding marinade, and pat dry. Heat olive oil in a large skillet over medium-high heat. Add chicken, and cook 6 minutes or until deep golden brown. Turn, and cook 2 minutes. Transfer chicken to a plate; discard excess drippings from pan.
6. Stir in chicken stock, scraping with a wooden spoon to deglaze pan. Pour sauce over Braised Leeks; set aside.
7. Preheat oven to 375°. Dredge chicken in mustard mixture, and arrange on top of leeks. Spoon any remaining mustard mixture over chicken. Top with breadcrumb mixture. Bake 40 minutes or until chicken is golden brown.