Begin with finely chopping the onion and the Serrano ham. Then place a pan on a medium-high heat and add the butter. Once it melts add the pancetta and cook until it begins to brown. Then add the onions, sweat down and add the Serrano. Cook for a further 2 minutes before adding the plain flour
Stir the flour well until it is cooked and slowly pour in the milk. Keep adding a stirring until you have a nice thick sauce. Grate in the nutmeg and season to taste. Let it simmer gently whilst stirring for 15-20 minutes
Line a baking tray with baking paper and add the sauce. Leave in the fridge to set for 4 hours
Then lightly dust a chopping board with flour. Slice the sauce into cubes and roll into balls in the flour
Beat two eggs, add the croquettes and then place in the bread crumbs. Make sure they are evenly coated
Then heat some vegetable oil to 180c/350f and fry until golden brown and crispy. Enjoy!