Peel and boil the potatoes in salted water for 10-15 minutes until tender, then drain. Alllow them to fully dry before mashing.
Mix the mashed potato with shredded ham hock, grated cheese, and chopped parsley. Season the croquette mixture with sea salt and cracked black pepper.
Take a small amount of croquette mixture into your hands and squeeze, then roll it into balls. Alternatively, make croquettes into oblongs or other shapes using a pastry scraper to help you.
How to breadcrumb croquettes
Place the flour, beaten egg, and the panko breadcrumbs into three separate bowls.
Dredge each croquette in the flour to coat the surface. Then dip them into the beaten egg, and then drop the croquette into the breadcrumbs and toss to completely coat each one.
How to deep fry ham croquettes
Heat the deep fat fryer to 180℃/355℉ or heat oil in a large saucepan to this temperature.
Deep fry croquettes in small batches until golden brown. Remove to a paper towel-lined plate to soak up excess oil before serving.
Dipping sauce
Combine the ingredients in a small bowl and serve alongside the Gruyere and ham hock croquettes.
Notes
I'd suggest serving 2-3 of these croquettes per person as an appetizer or first course. You can shape them smaller (gold ball size) to make canapes. If making a large batch, place them on a tray after frying and keep warm in the oven for 10-15 minutes on low heat (150C/300F) whilst finishing them all. They are best served fresh. If you want to make them in advance, stop and refrigerate after breadcrumbing. They also freeze well at this stage. You can cook from frozen, but I recommend finishing them off in the oven after getting a good color on them in the fryer to ensure they are heated through.