Finely chop the onion and the Serrano ham
Place a pan on medium-high heat and add the butter
Once butter melts, add the pancetta and cook until it begins to brown
Add the onions, sweat down and add the Serrano ham
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 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
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
Heat vegetable oil to 180°C/350°F and fry until golden brown and crispy
