Step 1: Cook the Pasta and Broccoli
Bring a large pot of water to a rolling boil. Add a very generous amount of salt (the water should taste like a mild seawater). Add the pasta and cook according to the package instructions, but set a timer for 3 minutes before it’s supposed to be al dente. When that 3-minute mark is reached, add the bite-sized broccoli florets to the pot with the pasta. Continue cooking together for the final 2-3 minutes until the pasta is perfectly al dente and the broccoli is bright green and crisp-tender. Before draining, carefully reserve at least 2 cups of the starchy pasta water. Drain the pasta and broccoli and set aside.

Step 2: Start the Sauce – The Roux
While the pasta is cooking, begin your sauce. In a large skillet, Dutch oven, or heavy-bottomed pot, melt the 4 tablespoons of unsalted butter over medium heat. Once the butter is melted and foamy, add the 4 cloves of minced garlic and the optional ¼ teaspoon of crushed red pepper flakes. Sauté for about 30-60 seconds, stirring constantly, until the garlic is fragrant. Be very careful not to let it brown or burn, as this will make the sauce bitter. Sprinkle the 3 tablespoons of all-purpose flour over the melted butter and garlic. Immediately begin whisking constantly. Cook the flour-butter mixture (this is your roux) for about 1-2 minutes. This step is crucial to cook out the raw flour taste. The mixture will look like a thick paste.

Step 3: Build the Cream Sauce
While still whisking, slowly begin to pour in the 2 cups of warmed whole milk. Add it in a slow, steady stream. It’s important to continue whisking vigorously as you add the liquid to prevent any lumps from forming. Once all the milk is incorporated and the sauce is smooth, pour in the 1 cup of heavy cream.

Step 4: Simmer and Season
Increase the heat slightly to bring the sauce to a gentle simmer, stirring occasionally. Allow it to simmer for 3-5 minutes, until it has thickened enough to coat the back of a spoon. Now, it’s time to season. Stir in the 1 teaspoon of salt, ½ teaspoon of black pepper, and ¼ teaspoon of freshly grated nutmeg. Nutmeg is a classic addition to cream sauces and adds a wonderful warmth and depth of flavor that beautifully complements the cheese.

Step 5: Melt the Cheeses
Reduce the heat to the lowest possible setting. It’s important that the sauce is not boiling when you add the cheese, as high heat can cause the cheese to separate and become oily. Begin adding the 1 ½ cups of grated sharp cheddar and ½ cup of grated Parmesan in small handfuls, stirring or whisking constantly until each addition is fully melted and incorporated before adding the next. Continue until all the cheese is melted and the sauce is velvety smooth and glossy.

Step 6: Combine and Finish the Dish
Add the drained pasta and broccoli to the pot with the cheese sauce. Gently stir everything together until the pasta and broccoli are evenly coated in the glorious sauce. At this point, the sauce might look a bit thick. This is where your reserved pasta water comes into play. Add about ½ cup of the starchy pasta water to the pot and stir it in. The starch in the water will help emulsify the sauce, making it extra creamy and helping it cling perfectly to every noodle and floret. Continue to add more pasta water, a tablespoon or two at a time, until the sauce reaches your desired consistency.

Step 7: Final Touches and Serving
Stir in the optional 1 teaspoon of lemon zest. This is a pro-level tip that doesn’t make the pasta taste lemony, but instead brightens up all the rich flavors and cuts through the creaminess, making the entire dish taste more vibrant. Taste the pasta one final time and adjust seasoning if necessary. Serve immediately in warm bowls, garnished with a sprinkle of fresh parsley and an extra grating of Parmesan cheese.