Chop the ham and mushrooms and sauté with the olive oil. Add the onion and the flour and stir continuously for three minutes. Heat the milk in a separate pan and slowly add to the mixture stirring continually and heat until the desired consistency is achieved which is quite thick.
Remove from the heat and allow to cool before storing in the fridge overnight.
Place some plain flour in a bowl. In a separate bowl, place some beaten eggs. Take small handfuls of the chilled mixture and roll into balls. First, dip into the egg mixture and cover fully, then roll into the flour and finally roll in and coat completely with the breadcrumbs.
Repeat this until have used all the chilled mixture.
Heat enough sunflower oil in a pan until hot to cover the croquetes, then place into the oil.
Cook for a couple of minutes on each side until golden. Remove from the oil and place onto some kitchen paper to soak up any excess oil then plate up and enjoy!