Step 1

Grate the potatoes lengthwise on a box grater, as you would grate carrots. Spread the potatoes and the grated onion out on a clean kitchen towel and roll it up like a jelly roll. Squeeze the towel to remove as much liquid as possible without breaking the potatoes. Transfer the potato mixture to a medium bowl, add the egg, flour, 1½ teaspoon salt and 1/2 teaspoon pepper and combine well.

Step 2

Heat a large cast iron skillet over medium-high heat. Add 2 tablespoons of butter and 1 tablespoon of the olive oil and heat until sizzling. Drop a scant ¼-cup measure of the potato mixture into the pan and repeat to make 6 latkes. Using a small metal spatula, lightly flatten each latke. Cook over medium to medium-high heat for 3 to 4 minutes, until the underside is golden brown. Turn the latkes with the spatula and cook on the other side for 2 to 3 minutes, until nicely browned. Transfer to a plate lined with paper towels.

Step 3

Add the remaining 2 tablespoons of butter and 1 tablespoon of olive oil to the pan and heat until sizzling. Repeat to make 6 more latkes with the remaining potato mixture and transfer them to a plate lined with paper towels.

Step 4

Sprinkle all the latkes lightly with salt, if desired, and serve warm with a dollop of sour cream or applesauce .