Wash potatoes and place them in a baking pan. Bake in a 200°C /390°F oven for about an hour until they are cooked. In a saucepan, melt the butter over medium heat. Add the flour and mix well with a whisk for 3-4 minutes. Add the milk and stir continuously with the whisk to dissolve any lumps.Cook for 5 minutes, on low heat, until the mixture binds well and becomes a velvety, slightly elastic, and firm béchamel. Remove from the heat and keep one cup for the recipe. When the potatoes are cool enough to handle, remove the potato skin and mash them with a potato masher or fork in a large bowl. Add the béchamel, kefalotyri cheese, oregano thyme, and spices. Mix well. Add sea salt and pepper to taste.If the mixture feels too loose, refrigerate for 30 minutes. Scoop the potato mixture into a small ball (about two tablespoons) and press one cube of feta into the center.Seal the potato ball tightly around the cheese. Repeat with the remaining mixture and cheese. In a bowl, beat the egg with a fork; in another bowl, mix the crushed chips and the breadcrumbs.
In a deep pot, heat plenty of sunflower oil over medium heat until hot.
Gently drop a potato fritter into the egg bowl. Next, pick up the fritter from the beaten eggs, give it a wiggle to get rid of any excess egg, and drop it into the bread crumbs. Then repeat one more time into the egg, wiggle, and add more breadcrumbs.
In a large skillet, heat the oil until shimmering. Add the fritters, two at a time (or more, depending on the size of your skillet), and fry until deep golden brown. It should take about one to two minutes for both sides, flipping as needed—transfer fritters on paper towels to absorb extra oil.
Serve potato fritters as a side to a steak, a roast, or a veggie casserole. Enjoy!