Cook the Pasta: Bring a large pot of salted water to a boil, add the shell pasta, and cook until al dente, about 7-9 minutes. Reserve ½ cup pasta water, drain, and set aside.

Prepare the Broccoli: Steam or blanch the broccoli for 3-4 minutes until tender. Drain and set aside.

Make the Roux: In a skillet, melt butter over medium heat, whisk in flour and cook for 1 minute.

Create the Cheese Sauce: Gradually whisk in milk or half-and-half, cooking for 3-5 minutes until thick.

Melt the Cheese: Stir in cheddar and parmesan until melted, adding garlic powder, salt, and black pepper.

Combine the Ingredients: Add chicken and broccoli to the sauce, stirring to coat and heat through.

Mix in the Pasta: Toss in the cooked shell pasta, mixing until combined, adding reserved pasta water if too thick.

Final Seasoning and Serve: Taste and adjust seasoning, serve hot garnished with parmesan or red pepper flakes.