In a bowl add the three cheeses and mix to combine. Set aside for now.
In a medium saucepan gently heat the butter until melted. Remove from the heat.
Add the plain flour in one go and beat with the spatula until there are no lumps and you have a flour paste (or roux).
Start to pour in the milk. begin with a few tablespoons first to loosen the flour paste. Gradually add all the milk beating hard to prevent lumps.TOP TIP: if you use a room temp milk, it's less hard work. Don't worry if the flour paste looks like a lumpy mess to begin with, it does this when it reacts with the cold milk but as you add more milk it will loosen to a béchamel (white) sauce.
Now you can return the saucepan to the heat and continue to stir while you cook the flour. This process eliminates the flour flavour to sauces.
The béchamel sauce will thicken as it warms through. You can now add the majority of the three cheese mix, keeping enough back to top your macaroni cheese.
Also add the mustard powder, garlic powder, Worchester Sauce and turmeric oil if using (you'll notice the improvement in colour immediately). Give the cheese sauce a good stir to combine all the ingredients.
Now tip the cooked macaroni into the cheese sauce and mix to coat all the pasta.
Grease your oven proof dish (this makes serving easier and washing up much easier!) Pour the macaroni cheese mixture into the dish and spread evenly. Finally top with the remaining cheese.
Pop the macaroni cheese under the grill for 5 minutes or more to achieve the optimum caramelised cheese topping.
Serve immediately with gluten free garlic bread if you needed more carbs in your life!