Utilize the grating disk of a food processor or the large apertures of a box grater to grate the potatoes and onions. Squeeze out the maximum amount of liquid using cheesecloth or a clean, lint-free dishtowel to transfer the mélange. What amount of liquid emerges will astound you.
Whisk together the flour, baking powder, salt, and pepper in a large mixing basin before adding the egg. While stirring, incorporate the compressed dry potatoes into the batter until they are coated evenly.
Preheat a substantial, heavy-bottomed skillet to medium-high temperatures and drizzle on an estimated 1/4" of oil, just sufficient to saturate the bottom of the pan. Apply the batter to the pan in a generous tablespoon increments (or utilize a trigger-release ice cream scoop) once the oil begins to shimmer. Immediately shape the batter into disks using a spatula. Fry for 4-5 minutes, or until the edges are browned. 3 to 4 minutes later, flip and cook until the second side is golden brown.
Repeat with the remaining potato mixture, re-greasing the skillet with additional oil if necessary. Serving heated latke with chives garnished in sour cream.