Mash potatoes then stir in cheeses, a few pinches, of seas salt and freshly ground black pepper and 1 egg. In a shallow bowl, lightly beat the other 2 eggs with a fork. Pour breadcrumbs into another shallow bowl beside it. Line a baking tray with baking paper.
Form potato mixture into about 24 balls and roll into slightly oblong shapes.
One at a time, dip croquettes into beaten eggs, letting excess drip off, then roll in breadcrumbs to coat. Place on baking tray as you make them.
Heat 120ml of oil in a large frying pan over medium-high heat. Fry croquettes in batches, turning until golden brown on all sides – about 5 minutes per batch. Add and heat a little more of each oil between each batch.
Transfer each batch to paper towels, sprinkle with chopped parsley and serve immediately.