Make sure you have a bowl of salted cold water for your potatoes so that they don't oxidize and turn brown on you.
Peel your potato (or potatoes if you're using more than 1) and have a grater ready.
Shred that potato and immediately put into the bowl/container with cold salted water. Set aside.
Then quickly small dice your onion and set that aside, as well.
In a medium heavy-bottomed pan, add enough vegetable oil to cover the pan by 1/2 an inch and heat under medium high heat.
Drain potatoes from water and squeeze out and excess water retained by the potatoes. Pat dry with paper towels.
In a small bowl, combine the shredded potatoes, onions, egg, baking powder, and flour. Season with salt and pepper. Mix well.
Fry the latkes in the oil until crispy and golden brown, about 2-3 minutes per side. Let drain on a paper towel-lined plate. Then, using the open end of a drinking class (or the reasonable option would be to use a cookie cutter), cut a nice even circle out of the latke. Then eat the edges, because they're delicious. Top with spicy tuna tartar if you want and even better treat!