On a box grater, coarsely shred the onion and potato. Transfer to a colander or wrap in a cheesecloth sling, and squeeze as dry as possible. Let stand for 2 minutes, then squeeze dry again. Put the potatoes in a large bowl, add the flour, salt, pepper, baking powder and egg, and gently fold to combine.
In a large cast-iron skillet, heat 2 tablespoons oil until shimmering. Drop heaping tablespoons of the potatoes into the skillet and flatten them with the back of the spoon. Cook the pancakes over moderately high heat until the edges are golden, 1 1/2 to 2 minutes. Flip and cook until golden on the bottom, about 1 minute. Drain on paper towels. Repeat with the remaining potatoes, adding more oil to the skillet as needed.
Serve the potato pancakes topped with Chunky Granny Smith Applesauce and a small dollop of Cinnamon Creme Fraiche.
Cook's Note: Reheat the pancakes in a single layer on a cookie sheet in a 400 degree oven until they're crisp again. If you undercooked them a bit or didn't get the browning on them you'd hoped for, you can compensate for this in the oven.
Chunky Granny Smith Applesauce:
To a large pot, combine 1 cup water, sugar, cinnamon, lemon zest, and apples. Bring to a boil over medium heat and cook until soft, 8 to 10 minutes. Taste for sweetness and add more sugar if desired. Coarsely mash to a chunky consistency. Let cool to room temperature.;
Cinnamon Creme Fraiche:
Whisk together creme fraiche and cinnamon, cover and refrigerate for at least 30 minutes to allow the flavors to meld.;