If there’s one dish that most Americans really should know but don't, it’s causa. It’s everything Americans love—mashed potatoes, tuna (or chicken, or some similar) salad, and potato salad—all compressed into one easy make-ahead casserole. It could be the ultimate all-American potluck dish, except that it’s entirely Peruvian.
I first learned of causa many years ago when a Peruvian cook I worked with named Felipe would sometimes make it for the staff. Years later I took a trip to Peru and ate several examples of it there. What becomes clear about causa after eating it just a few times is that it can come in many forms, but a few features are constant: causa is always served cold; causa always features a top and bottom layer of mashed potatoes that are seasoned with lime juice and aji amarillo (a spicy Peruvian chile pepper); and causa always contains a mayonnaise-y salad.
Beyond those basic qualities, causa can vary widely. For one thing, as already mentioned, the salad in the middle can be made with a wide range of meats or seafood—tuna, chicken, crab, or some other white meat or seafood—though tuna and chicken are the most common. And what’s in that salad can vary quite a bit, too. It could be as simple as the meat tossed with some minced onion and mayonnaise, but it could also include peas and carrots, or a layer of sliced avocado, or diced shrimp, or something else. Sometimes you’ll see black olives, or tomatoes, or chile peppers, or slices of hardboiled egg. And sometimes causa is served as a large casserole (making it the perfect potluck dish), while at other times it’s made into more elegant individual portions by stacking the layers inside a ring mold.
That's the best part about causa: You can and should have a lot of fun with it. Just use the basic template as your guide and feel free to play around with the rest.
The first step is to mash some potatoes. In Peru, they use a variety of yellow potato that we don’t have in the United States (nor do we have most of the other hundreds upon hundreds of potatoes native to Peru). Anyone not in Peru will have to use what they can find. I have a Peruvian friend who says Russets are the best option stateside, but I’ve also tested the recipe with Yukon Golds, and they work well, too.
Next, you will need aji amarillo paste, which is made from one of Peru’s most popular chile peppers. You can buy the paste premade in well-stocked Latin American grocers, but even better, if you can find it, is to start with frozen whole aji amarillos; they'd be in the freezer section of a very, very well-stocked Latin American grocer.
Simply steep the frozen peppers in boiling water for a few minutes to soften them, then trim away their stems and seeds. Put the pepper flesh in a blender and let it run until the purée becomes uniform and smooth; there's no need to add water or any other liquid. The paste made from frozen peppers is fruitier, brighter, and more complex than the one in the jar, so it’s worth making if you can find the frozen peppers.
To make the mashed potatoes, cook the potatoes either by baking, microwaving, or boiling them. Pass the cooked potato flesh through a ricer or food mill, add the aji amarillo paste, lime juice, and oil, and stir it in until the potatoes are an even yellow hue. This should be done while the potatoes are still somewhat hot, since they won’t mash well once fully cooled. Only after you’ve mixed everything together should the potatoes be chilled in the fridge.
For the filling, my recipe gives the option of either tuna or chicken, but you could of course use another appropriate meat, such as crab. Whichever you use, mix it with finely minced white onion and enough mayonnaise to make it soft and spreadable. Add-ins are up to you. Cooked peas and carrots are a common choice.
To form the causa, you can either make a large one in a casserole dish, or smaller individual ones. Start by spreading out an even layer of the mashed potatoes on the bottom of a casserole dish or on a plate, using a ring mold around it to help keep a cylindrical form. Next, add the salad filling, plus anything else you’d like to include. I show diced shrimp here with the tuna salad in the casserole dish, and thinly sliced avocado with the chicken salad on the plate; you could put the avocado with the tuna, or add olives or whatever else you may fancy.
On top of that goes the final layer of mashed potatoes. To finish it, you can garnish the top of the causa with whatever you think looks good, making little designs with additional ingredients, such as black olives, diced avocado, pieces of tomato, a drizzle of mayo, and a sprinkling of fresh herbs.
Once it’s assembled, a casserole-style causa can be kept refrigerated overnight, making it an excellent make-ahead dish for potlucks and such. It’s not an American dish, but it’ll fit right in next to the onion dip and mac and cheese.