Boil the potatoes: Add water and rock salt over high heat in a large pot and bring to a boil. Place the potatoes into the salted water, and boil for 10-15 minutes until soft.
Cheese slicing: While the potatoes are boiling, cut the Camembert cheese into 1” (2.5cm) sticks; once cut into pieces, place them in the freezer (just until you start forming the croquettes).
Drain the potatoes and transfer them to a large mixing bowl. Mash the potatoes roughly, add the beaten egg, salt, and pepper, and mash them together until smooth.
Coating mixture: Mix flour and Panko breadcrumbs in a wide top bowl or on a plate.
Prepare a platter or tray lined with parchment paper for the flour-coated croquettes.
Forming the croquettes: Take the Camembert sticks out of the freezer. Scoop 1 & 1/2 TBSP of the mashed potato into your hand, then create a ball. Press a stick of the Camembert in the middle of the mashed potato ball, wrap the mashed potato around the Camembert, and then gently mold and shape it into a Croquette shape. (see note #1 for tips) Croquette coating: Place the croquette into the flour and breadcrumb mixture and roll around. Ensure to coat well and transfer it onto the lined tray. Repeat until all of the mashed potato has been used.
Chill: Keep the Croquettes chilled in the refrigerator for at least an hour before frying.
Frying: Pour the cooking oil into a deep frypan over medium heat.Gently and carefully drop the Croquettes into the hot oil (placing them away from yourself to avoid any hot oil splashes).Fry in batches for around a minute or two until golden. (see note #2 for tips) Rest: As you remove them from the oil once cooked, rest them on a wire rack.