Lamb Fillet

Many thanks for your help, Ember. It’s a little hard to answer your first question, though. The piece is about 12 inches long and about an inch deep, weighing in at 16 ounces. Does that help? I’ve a feeling it’s a boned loin (but not too sure).
Does this mean (as per your explanation of temperature equilibrium) that ~55C for a minimum of an hour sounds about right?