Switch on the instant pot to saute and add the butter and flour. Stir continuously until the flour is slightly browned in the butter. Add a few splashes of milk to keep it from sticking to the pot (2 minutes). Cancel saute.
Add the macaroni, broth, garlic powder, black pepper, chilli flakes, sea salt and rosemary. Close the lid, make sure the steam release handle is sealed and press the pressure cooking button. Set the timer to 4 minutes. Once the pot beeps, do a quick release and open the pot. Remove the rosemary sprigs.
Add the broccoli and cook for 4-5 minutes or until the broccoli is slightly tender. Add a little broth or water if there is less liquid for the broccoli to cook.
Add the milk, half and half, cheddar and parmesan (if using) and cook for two minutes or until the cheese has melted and coats the pasta. Mac and Cheese is ready to be served.
Use sharp or extra sharp cheddar for maximum flavor and taste.
Substitute the vegetable broth with chicken broth if you want to.
Instead of rosemary, add any other herb of your choice.
You can sub the fresh milk with evaporated milk as well.
If you don't want to use Parmesan, add mozzarella or Monterey Jack.
Skip the broccoli if you don't care for it.
Store the leftovers in a covered container in the refrigerator.
Reheat the mac and cheese in a saucepan on gentle heat with a few tablespoons of milk added to it to make it smooth again.