Boil the water with the salt. Once heavily boiling add the pasta and let cook.
Take out of the water once al dente and if the sauce is not ready yet add a tbsp of butter and mix so they don't stick to each other.
Melt the butter and add the flour. Whisk them together over medium heat and let them cook for a minute starting from the point where they start to bubble.
Take off the heat and add the milk little by little, whisking in between. This helps avoid lumps forming.
Take back to medium heat and cook while we stir with the whisk. Once it has started to boil you can turn off the heat since it means the flour has now completely cooked.
Add the cheeses and mix until completely melted.
Taste and adjust the level of salt and add pepper.
Mix the sauce with the macaroni.
Put the mac and cheese in individual over-safe dishes or a large dish so everyone can take some.
Mi the panko with the butter and salt and sprinkle over the dishes.
Take to the oven on broil until golden.