minutes. Add the butter, thyme, and shallots, reduce the
heat to medium, and continue to cook, turning and
flipping the lamb occasionally, and basting regularly with
the browned butter (to baste, tilt the pan toward you so
that the butter pools at the bottom and spoon the butter
over the lamb, taking care to hit any underbrowned spots
repeatedly), until the lamb is deep golden brown and an
instant-read thermometer inserted into the thickest part of
each rack section registers 120°F for medium-rare, or
130°F for medium, 3 to 7 minutes longer. Transfer the
lamb racks to a rack set on a rimmed baking sheet and let
rest for 5 minutes.
To serve, reheat the fat in skillet until smoking and pour
over the lamb to warm it. Carve and serve immediately.