Add the whole milk, water, butter, salt, and pasta to a large skillet over low-medium heat. Bring to a low simmer and cook for 8 minutes (if using white pasta, cook for 6). Stir occasionally.
When the pasta is al dente and most of the liquid is absorbed, add the garlic powder (and optional dijon mustard) and stir well, then stir in the cheese and remove the pasta from the heat. Stir well to ensure it doesn't stick to the bottom.
Add the cooked or thawed broccoli and cover for about 1 minute to warm it up. (Or heat it in the microwave instead.)
Stir well and top with red pepper flakes and fresh cracked black pepper to taste. Enjoy!
Notes
You can use any cheese here, but extra sharp cheeses don't melt as well and tend to leave a grainy texture. I use a mixture of mild cheddar and Unexpected Cheddar (which is a sharp cheddar-Parmesan blend), but you can go for gruyere, Monterey Jack, Pepper Jack, or whatever cheese you prefer! Buy it in blocks and shred it yourself for the highest melting potential.