Preheat your oven to 350° F. It’s important to have the oven hot and ready for baking once your mac and cheese is assembled.
Cook the elbow macaroni in a large pot of salted boiling water, but keep in mind to cook it for about 3 minutes less than the package directions indicate. You want it al dente as it will continue to cook in the oven. Once done, reserve half a cup of the pasta water, then strain the pasta.
While the pasta is cooking, place the whole milk and fresh spinach in a blender. Blend on high speed until completely smooth. This step is crucial as it gives the dish its vibrant green color and subtle spinach flavor.
In a large pot over low-medium heat, melt the unsalted butter. Add the flour and whisk continuously for about 2 to 3 minutes to create a roux. It should look smooth and slightly golden.
Slowly whisk in the milk and spinach mixture, ensuring there are no lumps. Bring this mixture to a gentle boil while stirring frequently. This is where the magic starts to happen!
Once it reaches a boil, reduce the heat and let it simmer for about 3 to 4 minutes, whisking occasionally. You’ll notice the sauce will begin to thicken and bubble gently.
Now, it’s time to make it cheesy! Add the reserved pasta water and the white cheddar cheese to the pot. Whisk until the cheese is melted and the sauce is creamy.
Stir in the cooked elbow macaroni, kosher salt, broccoli florets, and peas. Mix everything until well combined, making sure the pasta is evenly coated with the cheese sauce.
Transfer the entire mixture to a greased 13 x 9-inch baking dish. Spread it out evenly and pop it in the preheated oven.
Bake for about 20 minutes, or until the cheese is bubbling and the pasta is set. At this point, your kitchen will smell heavenly!
