1/2 cup 2% reduced-fat milk
2 tbsp. butter
1 tsp. baking powder
4 1/2 oz. all-purpose flour
1/2 tsp. freshly ground black pepper, divided
1/4 tsp. kosher salt, divided
3 cups unsalted chicken stock
2 cloves garlic, minced
1 medium onion, chopped
2 carrots
2 stalks celery
2 tbsp. chopped fresh tarragon, divided
2 tbsp. chopped fresh thyme, divided
1 tbsp. olive oil
1 pound skinless, boneless chicken breast halves