1. Preheat oven to 400 degrees.
2. Mix breadcrumbs,herbs,salt and pepper to taste in processor.
3. Rub lamb generously with mustard then coat with breadcrumb mixture, pressing to adhere.
4. Arrange racks in roasting pan; roast until outside is crisp but inside is still pink, 20 to 25 minutes; do not overcook.
5. Blend yolks,cheese,lemon juice,cornstarch and 1/4 t. salt in processor until smooth.
6. With machine running, add butter through feed tube in thin stream.
7. With machine running, add cream through feed tube in thin stream.
8. Transfer to saucepan and keep warm in tempid water bath.
9. Cut racks into ribs; arrange 4 ribs on each plate.
10. Spoon sauce over and serve immediately.