# Mathematics for Real-World Systems Centre for Doctoral Training

My gift to you is to translate a funny Instagram postLink opens in a new window containing the recipe of how to make a great Carbonara*

### Carbonara, or the domain of definition in the kitchen

In Maths, when studying a function you must specify the set of real numbers on which the function can be evaluated, the domain of definition (in Italian, we call it field of existence). You find it more or less like this: for every x that belongs to an interval. This means that there is a well-defined space where you cannot twist things, where things either exist or don't.
Saying things like "I make carbonara with cream", "I use bacon because I prefer a smoky taste", "I cook the egg because I am afraid of salmonella" is not allowed.

No, unlike some summer flings, Carbonara gives you certainties in life.

Carbonara is only defined in the domain where you can find these ingredients:

• 200g of pasta (serves 2) - pasta has to be in the shape of spaghetti or rigatoni.
• one yolk and a half for each person (I know, there is some complicated maths here)
• 100g of guanciale
• 50g of Roman pecorino
• 30g of parmesan (optional)
• ground black pepper, ideally grounded on the spot

... nothing else!

The procedure:
- boil your pasta in not too much water, this way there is going to be a higher concentration of starch in the water.
- sautÃ© guanciale until it's crispy, not chewy,
- remove it from the pan and put it aside but leave that greasy fat in the pan.
- eggs: they must be fresh if you don't want to cook them. Whip the yolks with a fork, then add pecorino and pepper. You should obtain a medium solid batter.
- 3 minutes before the end of the given cooking time (cooking times are obviously al dente) use a skimmer to transfer the pasta to the pan, where all the melted fat lies.
- add some of the starchy water you used to cook the pasta, stir it until creamy for the remaining cooking time.
- after this, remove from stove. I'll repeat: remove from stove. Add the batter and the crispy guanciale to the pan and stir vigorously.

Buon appetito

*I apologise to vegans, vegetarians and all readers with dietary requirements: the post is supposed to be funny, it doesn't mean that you cannot twist the recipe to make it good for you, but try to follow the steps as closely as you can for best results!