Beer can be confusing to measure: Do you include the head, or scoop it off, or let it dissipate? Guinness comes in a variety of different-size cans and bottles. Tilt the measuring cup while pouring the stout against the side of the measure (to minimize the creation of its famous head), and let the foam subside so that you are only measuring the dark liquid. Any leftovers are the cook’s treat.
To crush coriander seeds and peppercorns, either use a mortar and pestle, or put coriander seeds and peppercorns in a resealable plastic bag and crush them with the bottom of a heavy skillet or a rolling pin.
Glaze can be made 3 days ahead and chilled, covered. Bring it to room temperature before using.
Depending on where you buy your lamb rib chops, they can come trimmed and frenched (the bones are scraped clean of fat and meat), or left alone with the thin layers of fat and meat on the bones intact. It is generally cheaper to buy 8-rib racks of lamb from the big-box stores and cut them yourself into chops. If you prefer the look of long, cleaned bones, select the frenched chops or racks (some big-box stores sell them that way). If you want extra nibbly bits of meat and fat left on the bone for your guests to gnaw on, look for untrimmed chops, or specifically request the butcher not to french the bones.