Thin ribbons of aromatic mint complement the richness of this stout-spiked gravy, and add a welcome touch of green. Serve with plenty of fluffy mashed potatoes.

This luxurious marriage of lobster and cream—so-named because it is rich, expensive, and subtly perfumed with Irish whiskey—is traditionally served in lobster shells; but it also makes a quick and sumptuous sauce for pasta. When...