1 (16-ounce) package penne pasta
1 (10-ounce) package baby spinach
1 yellow onion, chopped
5 cloves garlic, finely minced
12 tablespoons butter, diced
1-1/2 tablespoon olive oil
1 teaspoon red chili flakes
4-1/2 cups milk, warmed for 2 minutes in the microwave
3/4 cup all-purpose flour
2 teaspoons salt
1/2 teaspoon black pepper, freshly ground
3/4 cup Gruyère cheese, freshly shredded, or more to taste
2 tablespoons flat-leaf parsley leaves, chopped

Preheat the oven to 400°F. For the penne pasta: Bring about 8 quarts of water to a boil. Add the pasta, bring back to a boil, and then immediately lower the heat to a gentle boil. That way the pasta is cooked all the way through evenly. Cook the pasta for about 10-12 minutes total. Salt (with 2/3 teaspoon) the water half-way through the cooking process (it will bring out the natural flavor of the pasta and the pasta will be more tender) and keep stirring every now and then so the pasta doesn’t stick to the bottom. It may take longer than the cooking time that’s written on the box. When the pasta is cooked (cooked inside and out but still in shape and firm), reserve about 1/3 cup to 1/2 cup of pasta water and drain the pasta (do NOT rinse). Transfer it to a large flat platter. In a large sauté pan or a large wok, heat the oil. Add the chopped onions and cook until they’re slightly golden. Add the penne pasta and 2 tablespoons of butter. Toss the pasta using 2 large spoons on each side of the pan for about 3-4 minutes. Season with 1/2 teaspoon of salt and 1/2 teaspoon of pepper. If the pasta starts sticking to the bottom, add a little pasta water. Transfer to a large serving platter. Sprinkle with about 1 tablespoon of flat-leaf parsley.

For the Spinach: Wash the spinach thoroughly in a large bowl of water. Drain, then remove all the excess water using a salad spinner. Roughly chop all the spinach leaves. In the same wok, add the minced garlic and 2 tablespoons of butter. Cook the garlic for about 2 minutes until golden brown. Add the red chili flakes. Cook for another minute. Add another 1/3 of the amount of spinach to the pan, constantly lift the spinach leaves using 2 slotted spoons on each side of the pan. The leaves will start to wilt after 30 seconds or so. Add the other 1/3 of the spinach and repeat the same procedure for 30 seconds. Season with about 1/3 teaspoon of salt (this will prevent the spinach from changing color and will keep it bright green color). Repeat one more time with the rest of the spinach, then transfer the greens, with as little liquid as possible, into a large bowl. Reserve the excess spinach liquid in a separate bowl.

Reserve about 1/2 cup of spinach for the baking dish and add the spinach to the pasta. Toss well. Set aside.

For the béchamel sauce: In a saucepan, melt 8 tablespoons of butter over medium-low; you don’t want the butter to burn. Bring the heat back up to medium-high (the butter should be hot and golden) and add the flour. Keep stirring manually with a whisk for approximately 3 minutes. The flour should absorb the butter instantly and form a paste. Add the spinach liquid; stir well until incorporated and add the milk in 3 stages. Increase the heat while constantly stirring for about 5 minutes. Reduce the heat to low. Season with 1/2 teaspoon of salt and 1/4 teaspoon pepper. Let the sauce rest until it’s time to assemble the dish.

Assembly time: In a 14” x 10” x 3” high rectangular pan lined with aluminum foil and sprayed with oil (for an easy clean up), spread a layer of spinach. Add the spinach penne pasta. Spread ladles of the béchamel sauce. It should cover the whole tray and sprinkle with Gruyère cheese. Bake in the oven for 5 minutes at 400°F and broil for about 2-3 minutes to get a nice golden top. Remove from the oven and let it rest for at least 15 minutes. Cut into squares, and garnish with flat-leaf parsley. Bon appétit!