Preheat oven to 425°. Stir together the crème fraiche, horseradish and ½ teaspoon salt in a bowl and chill until ready to serve.
In a mortar and pestle crush the peppercorns. Transfer the crushed pepper to a bowl and stir in the panko, minced garlic, melted butter, rosemary, thyme, lemon zest and remaining 1 ¼ teaspoon salt until well mixed.
Place the lamb, fat side up, on an aluminum lined cookie sheet. Spread 1 tablespoon of the Dijon mustard over the fat side of each fat side of the lamb racks. Top with the panko mixture, pressing to adhere.
Bake at 425° for 30 to 35 minutes. Cover loosely with aluminum foil after 20 minutes if necessary to prevent the crust from burning.
Let it stand for 5 minutes before slicing.
Cut the rack into single or double chops. Serve alongside the horseradish crème fraiche.