Combine mustard, peppercorns and 1 Tbsp oil. Reserve. Heat remaining 1 Tbsp oil in a large skillet over medium heat. Season halibut with salt and pepper. Add halibut to skillet brown on both sides. Transfer to baking dish and bake for 5-7 minutes.
For sauce, heat butter in a skillet over medium heat, add leek and sauté 2-3 minutes. Add mustard, wine, and cream, increase heat and simmer until thickened (about 2-3). Add lemon juice. Season with salt and pepper.
Chef’s Note: Chardonnay works well with the leeks and pommerey mustard