Bring a large pot of water to a boil and season generously with salt. Add the pasta and cook until just under al dente, leaving a little bite in the center.

Before draining, reserve 1 cup of the pasta cooking water. Drain the pasta and set it aside.

Meanwhile, melt the butter in a large, shallow, broiler-safe enameled cast-iron pan over medium heat.

Add the flour and stir continuously to form a roux. Cook for about 2 minutes, until the mixture turns lightly golden and the raw flour flavor has cooked out.

Gradually stir in the evaporated milk. Whisk as needed until the sauce is completely smooth and free of lumps.

Add the onion powder, garlic powder, minced garlic, kosher salt, and black pepper. Stir well and adjust the seasoning to taste.

Continue cooking for about 3 minutes, stirring occasionally, until the sauce begins to thicken.

Reserve about 2 handfuls of the shredded cheeses for the topping. Add the remaining mozzarella, Monterey Jack, and Parmesan to the sauce. Stir over gentle heat until almost completely melted and smooth.

Fold in the drained spinach and marinated artichoke hearts, stirring until evenly distributed throughout the cheese sauce.

Add the cooked pasta and gently stir until every piece is coated. If the sauce is thicker than you prefer, add a splash of reserved pasta water until it reaches a silky consistency.

Sprinkle the reserved cheese evenly over the Spinach Artichoke Mac and Cheese.

Place the pan under the broiler for 4–6 minutes, watching carefully, until the cheese is melted, bubbly, and lightly browned. Serve immediately.