Crusted Fresh Herbed Rack of Lamb with Potato Leek Gratin and Roasted Garlic Sauce

Name: Crusted Fresh Herbed Rack of Lamb with Potato Leek Gratin and Roasted Garlic Sauce
Ingredients: 4 baking potatoes, like russets; 4 small leeks, white part only; 1 tablespoon unsalted butter, room temperature; 1 tablespoon chopped garlic; 1/2 quart heavy cream; Salt; White pepper; Nutmeg; 2 racks of lamb, fat cap removed, frenched; 3 tablespoons olive oil; 1 cup Dijon mustard; Salt and freshly ground black pepper; 1 tablespoon chopped fresh thyme leaves, plus 1 tablespoon; 1 tablespoon chopped fresh rosemary leaves; 1 tablespoon chopped fresh sage leaves; 1 tablespoon chopped fresh chervil leaves; 1 tablespoon chopped fresh parsley leaves; 20 cloves garlic, peeled; 1 cup dry white wine; 2 cups lamb stock or veal stock; 1 tablespoon butter