Grate the peeled potatoes and onion using a box grater or a food processor with a grating attachment.
Place the grated potatoes and onion in a clean kitchen towel or cheesecloth and squeeze out as much excess liquid as possible.
In a large mixing bowl, combine the grated potatoes and onion.
Add the eggs and mix well.
Stir in the flour, salt, and black pepper, mixing until the ingredients are well combined. The mixture should be thick and hold together; if it's too watery, add a little more flour.
In a large skillet, heat about 1/4 inch (0.6 cm) of vegetable oil over medium-high heat until hot.
Drop spoonfuls of the potato mixture into the hot oil, flattening each spoonful with the back of the spoon to form a pancake.
Fry the deruny for about 3-4 minutes per side, or until they are golden brown and crispy.
Use a slotted spoon to transfer the fried pancakes to a paper towel-lined plate to drain excess oil.
Repeat with the remaining potato mixture, adding more oil to the skillet as needed.
Enjoy your meal!