夫妻肺片 (fū qī fèi piàn) is a Sichuan cold dish. Despite its literal translation, "married couple [夫妻] lung [肺] slices [片]", it usually doesn't contain any actual lung. It does, however, contain other offal, usually tripe and/or tongue and/or heart. These are simmered in a savoury broth along with some braising beef, then everything is drained, cooled, sliced, and served cold, bathed in a spicy sauce and garnished with sesame seeds and maybe some peanuts.
To make it at home, try Helen Graves' interpretation of Fuchsia Dunlop's recipe. This is the recipe I followed, though due to a slight confusion over the amount of salt I actually used 2 tsp, which was a little too much, leaving me with rather salty yet still edible leftover stock. Also, I hate making caramel, so I used jaggery instead of rock sugar and didn't bother caramelising it. (Jaggery is an unrefined cane sugar that has a fantastic flavour — I buy mine from Indian supermarkets.) As Helen mentions, the leftover stock after braising is useful for soups and things, so don't throw it away!
Regarding the main ingredients, Helen just used beef, since her local shops were out of offal. If you do manage to get hold of some tongue, Kok Robin has some tips on cooking it. I used braising beef and tripe, both purchased from Morrisons supermarket. I'm not sure the tripe I used was ideal, since it was precooked and seemed very soft. I didn't simmer it for the full hour and a half as I was worried it might fall apart; I gave it 45 minutes in the end and it was OK, if much softer than I'd prefer. It probably wasn't actually the right kind of tripe, either; when I've had this dish in restaurants the tripe has been honeycomb tripe (as pictured above), and this definitely wasn't honeycomb tripe.
Finally, I definitely recommend that you use a good chilli oil in the dressing. I like to make my own, following Sunflower's recipe.