Wash and chop the leek into small pieces and poach it in a pan with a drizzle of olive oil.
Add the flour and stir constantly until brown. Add the warm milk little by little and stirring with a whisk, until the dough thickens. Add a pinch of nutmeg and salt.
Dice the cheese and add it to the dough, mixing well.
Put the dough in a dish, cover with transparent film and let it cool.
Make the croquette shape with our hands and we pass each croquette through a well-beaten egg and the bread crumbs.
Fry the croquettes in plenty of olive oil and let them rest on absorbent paper before serving.