Start by seasoning the chicken thoroughly with sea salt in a large bowl. Leave the chicken uncovered in the refrigerator overnight.
When you're ready to cook, let the chicken rest at room temperature for approximately 20 minutes. While it rests, preheat your oven to 450°F.
In a large skillet set over medium heat, add the dry coriander seeds. Roast them for 2 to 3 minutes, stirring or shaking frequently, until they become fragrant. Next, crush them in a mortar and pestle or a coffee grinder.
Now, in an oven-safe skillet or Dutch oven, place the chicken and roast it uncovered for 25 to 30 minutes. Once done, remove it from the oven and set it aside to rest.
In the same Dutch oven, add the shallots and grapes to the rendered fat in the pan. Stir them regularly until they soften. Then, add the crushed coriander seeds and chicken broth.
Add the mustard and let it simmer until it reduces by half, usually for 5 to 7 minutes. Afterward, season with additional salt and black pepper, and then stir in fresh thyme.
To serve, arrange the chicken on a plate, pour the sauce over it, and garnish with grapes.