Peel the Russet potatoes and the large onion, then grate them using the fine side of a box grater.

Transfer the grated potatoes and onion into a clean kitchen towel. Squeeze out as much moisture as possible.

In a mixing bowl, combine the potato-onion mixture with the flour, baking powder, sea salt, black pepper, and the egg. Fold until evenly incorporated.

Pour enough oil into a large skillet to cover the bottom, about ¼ inch deep, and heat over medium-high heat.

Scoop tablespoons of the latke mixture into the hot oil and fry for about 3-4 minutes on each side until golden brown.

Transfer the latkes to a paper towel-lined plate to drain excess oil while sprinkling with a pinch of sea salt.