Preheat oven to 425 degrees. Wash and scrub the outside of the potatoes or peel them if you'd prefer. Grate potatoes on the large holes of a box grater or in the food processor using the grating attachment. Place grated potato in a large bowl and toss with a 1/2 tsp salt. Set aside for 5 minutes.
Finely chop or grate the onion. Drain any excess liquid from the grated potatoes then place them in a large kitchen towel and squeeze out as much liquid as you can.
Mix grated potato with onion, eggs, remaining 1/2 tsp salt, flour/corntarch, and pepper in a large bowl until well combined.
Add 2 tablespoons of oil to a 12-inch skillet or cast iron pan over medium-high heat. (A 10-inch pan will work too but your pancake will be thicker.) Make sure oil is hot by placing a tiny peice of potato in the pan. If it sizzles, it's ready to go. Toss the potato mixture together one more time to make sure all the ingredients are well combined and any egg that settled to the bottom in reincorporated. Spoon potato mixture evenly in the pan then press down with the back of a spatula. Turn heat down to medium and cook until the edges of the pancake look golden brown, about 5 to 8 minutes
Drizzle remaing 2 tablespoons of oil over the top of the pancake then place in the oven. Bake for 15 minutes then broil the top until it's very well browned. Flip the big latke onto a serving plate or cutting board. Sprinkle a pinch of coarse salt over the top while it's still warm. Slice into wedges and serve with sour cream or plain Greek yogurt and applesauce.