Penne With Spinach and Ricotta

Fill a pot for the pasta with about 6 quarts of water, place over high heat, and bring to a boil.

Put about 1 inch of water in a pot large enough to cook the spinach. Place it over high heat. When the water boils, add 1 tsp. salt and the spinach. Cook until the spinach is quite tender, 5 to 6 minutes. Drain in a colander and squeeze out as much water as possible by pressing on the spinach with a spoon. Transfer the spinach to a cutting board and finely chop it.

While the spinach is cooking, peel the onion and finely chop it. Put the butter in a 12-inch skillet, add the onion, and place over medium-high heat. Sauté the onion until it turns a rich golden color, about 5 minutes.