Clean and wash the leek, cut it in half lengthwise and cut it into pieces of about 10 cm. Cut the leek pieces into fine strips. Boil up about 2 litres of salted water. Add spaghettini and leek strips and cook for 5-8 minutes.
Shrimps, except for the tail, loosen from the shell, scratch the back and remove the intestines. Wash the shrimps and pat them dry well. Peel garlic and chop finely. Heat the oil. Steam garlic until transparent.
Add the prawns and fry over medium heat for about 5 minutes, turning. Season with salt and pepper. Put the noodles and leek on a sieve, drain well and return to the pot. Spread truffle butter in flakes on top and mix with noodles and leek while tossing.
Place on a preheated plate. Arrange the prawns on top and serve immediately.