Once potatoes are slightly warmer than body temperature, add in the ham, scallions, egg, and any other mix-ins or cheese. Season if needed and combine until thoroughly mixed. Divide the croquette filling into 6 balls.
Using the palms of your hands, roll the mixture into football shaped balls. Gently form the patties by pressing between the palms of your hands or using a small plate wrapped in cling film. Once all the croquette patties are formed, cover and chill for 15-30 mins, up to 1 hour. This is an important step to ensure the croquettes will not explode when frying.