1. REPARE THE CROQUETTE FILLING: Preheat the milk in a pot. In a separate pot, melt the butter. When butter starts to foam add the serrano ham dices and sauté for 2-3 min. Add flour and stir. Add hot milk and keep stirring while bringing it to boil. Simmer for 7-8 min. Add the cheese and season with the chives, salt & pepper. Pour it on a tray and let it cool completely. Shape the croquettes.