Peel the potatoes and onions using a potato peeler and cut them in half. Make sure you do not cut the potatoes and onion into smaller pieces, otherwise you will not be able to grate them easily.
Now run the mashed vegetables through the food processor fitted with shredding blades to finely chop them. If you do not have a food processor, use a grater box to grate the onions and potatoes just like you would a block of cheese. Never slice the vegetables since they will not cook in the short amount of time it takes for potato pancakes to brown.
Place a thin tea towel or muslin cloth in a large bowl and transfer the grated onions and potatoes to it. Twist the top of the towel/cloth together to wring out as much liquid and starch from the grated veggies as possible. Keep twisting the towel until you can’t twist it any more.
Put the onion and potato mixture in a medium sized bowl and mix three lightly beaten large eggs with a fork until well blended.
After mixing the veggies and eggs thoroughly, add all purpose flour to the mixture and mix well.
Season the mixture with salt and pepper and set aside.
Pour about two tablespoons of olive oil into skillet and heat over medium.
When the oil is hot enough (not smoking), scoop out two heaping tablespoons of the mixture into the skillet. Press the mixture with the back of the spoon to give it the shape of a flattened disc ½ to 1 inch thick.
Fry for five minutes on each side or until nicely brown, and then move to a plate lined with paper towel to drain excess oil.
Top your pancakes with a little butter and sour cream before serving them.