3 large potatoes (2 pounds), such as russets, peeled
1 medium onion
1 large egg, beaten
3 tablespoons all-purpose flour, plus more if needed
1 tablespoon kosher salt
1/2 teaspoon freshly ground black pepper
1cup grated Asiago or mozzarella cheese (about 4 ounces)
1/4cup neutral oil, such as canola or grapeseed, for frying
3 tablespoons unsalted butter
Instructions
Preheat the oven to 200°F.
On the large holes of a box grater or in a food processor using the grating disk, grate the potatoes and onion. Working in batches, spin the potatoes and onion in a salad spinner to remove all excess water. Alternatively, wrap the potatoes and onion in cheesecloth or a clean kitchen towel and squeeze out the excess water.
In a large bowl, combine the potatoes and onion, beaten egg, flour, salt, and pepper and stir to incorporate. If the mixture is still watery, add another tablespoon of flour.
Scoop 2 tablespoons of the potato mixture onto a clean work surface. Press a few pinches of cheese on top. Add another tablespoon of the potato mixture on top of the cheese and press to cover the cheese while forming the mixture into a patty.
Line a baking sheet with paper towels and set a wire rack on top. In a large cast-iron skillet, heat the oil and butter over medium heat until the butter melts and the oil is hot. Carefully drop 5 or 6 patties into the hot oil. Fry for 3 to 4 minutes, until the bottom is golden brown, then flip and cook for 3 to 4 minutes more on the other side. Transfer the frico to the prepared baking sheet and place in the oven to keep warm. Repeat with the remaining patties. Serve immediately.