Make a breading station by filling 3 bowls with the following: Flour, beaten eggs and panko.
Using the cooled mashed potatoes, form croquettes into balls and then dip each one first in flour, then in egg, then in the panko. Place the breaded potato croquettes onto a plate and transfer to the fridge for 10-15 minutes.
In a high-sided pan, heat oil over medium-heat. Making sure not to crowd the pan, add the croquettes and cook for approximately 1-2 minutes per side, until golden and crispy.
Remove them with a slotted spoon and place them on a paper towel-lined plate to catch the excess oil. Continue to cook the remaining croquettes.
Serve with your favourite aioli sauce!