1 Preheat the oven: to 425ºF. Have on hand a 9- x 13-inch or 2-quart, shallow baking dish.

2 Cook the potatoes: Wash and cut the potatoes into 1-inch chunks (peeling optional). Place them in a large pot. Fill the pot with cold water until there is about an inch of water above the potatoes.

Add 2 teaspoons salt and taste; the water should taste as briny as the sea. If it doesn’t, add a few more pinches of salt.

Bring to a boil over high heat. Reduce the heat to a simmer and cook the potatoes, uncovered, for 15 to 20 minutes, or until tender when pierced with the tip of a paring knife.

Drain in a colander and return to the potatoes to the pot. Set the pot over low heat and stir the potato chunks for 1 to 2 minutes to dry them.

3 Mash and season the potatoes: Add the butter to the pot of hot, drained potatoes (still over low heat) and mash well with a potato masher until the butter melts. There may be a few ‘rustic’ lumps. Push the potatoes to one side of the pot to make a space for the milk. Add the milk and heat it until hot (this only takes a few seconds.)

Use a sturdy whisk to stir in the milk, whisking until the potatoes are fluffy and adding more milk, 1 tablespoon at a time, if the potatoes seem dry. Stir in 1/2 cup of the cheese, 1/2 teaspoon salt and 1/8 teaspoon pepper. Taste, and add more salt, if you like.

4 Meanwhile, make the filling: In a large skillet over medium heat, heat the oil. Add the onions and garlic and cook for 5 minutes, or until softened. If the onions are cooking to fast reduce the heat to medium-low.

Add the oregano and cumin, and cook for 30 seconds. Add the beans, corn, chicken, and salsa to the skillet. Stir in 1/2 teaspoon salt. Taste and add more salt, if you like.

5 Assemble the casserole: Transfer the filling to the baking dish. Spread the mashed potatoes over the top and sprinkle with the remaining 1 cup cheese.

6 Bake the casserole: Bake for 25 to 30 minutes, or until the filling bubbles and the cheese is golden. Leftovers will keep in the fridge for up to 3 days.