1-First step: Get all your ingredients prepped and ready. This recipe moves quickly once you start cooking! Thinly slice your baby bella mushrooms and white onion. Mince the garlic thoroughly to ensure even flavor distribution. If using fresh broccoli, cut it into bite-sized florets. Measure out all your remaining ingredients, especially the cheeses, which must be freshly shredded from blocks to prevent graininess in the sauce.

2-Second step: Heat 2 tablespoons of butter in a large stockpot over medium-high heat. Once the butter is melted and bubbling, add the sliced mushrooms. Let them cook undisturbed for the first few minutes to achieve a proper golden-brown color. Continue sautéing for 5-7 minutes total until nicely browned. Add the thinly sliced white onion and cook for another 3 minutes until softened. Finally, add the minced garlic and cook for 2 minutes until fragrant, being careful not to burn it.

3-Third step: Add the uncooked pasta, 4 cups of water, 1 1/2 cups of half and half, 1 teaspoon of Dijon mustard, 1/8 teaspoon of crushed red pepper flakes, and season with fine sea salt and freshly-ground black pepper to taste. Stir everything together to combine. Bring the mixture to a boil over medium-high heat.

4-Fourth step: Once boiling, reduce the heat to medium. If using fresh broccoli: Stir in the broccoli florets now. If using frozen broccoli: Set it aside for now as you’ll add it later with the cheese. Cook the mixture uncovered, stirring occasionally to prevent sticking, until the pasta is al dente according to package directions (typically 7-8 minutes).

5-Fifth step: Check the liquid level in the pot. If more than 1/2 cup remains, remove the excess with a ladle but reserve it in case you need to adjust the sauce consistency later. If using frozen broccoli: Steam it according to package directions, drain thoroughly, and set aside to add with the cheese.

6-Sixth step: Turn off the heat completely. This is important for allowing the cheese to melt properly without becoming grainy. Stir in the 2 cups of freshly-shredded sharp cheddar cheese and 1/2 cup of freshly-grated Parmesan cheese. Continue stirring until all the cheese is fully melted and the sauce is creamy. If you’re using frozen broccoli, add it now along with the cheese.

7-Step seven: Assess the consistency of your sauce. If it’s too thick, add the reserved liquid back in 1 tablespoon at a time until you reach your desired consistency. This is where the starchy pasta water works magic to create a perfectly creamy sauce.

8-Final step: Taste and adjust the seasoning with additional salt and pepper as needed. Serve the one pot broccoli mac and cheese immediately while it’s hot and creamy. The dish serves 4-6 people, making it perfect for family dinners or meal prep.