Start by preheating the oven to 400°F, using the convection bake option if available. Proceed by placing a 9x13-inch baking dish in the oven to preheat.
Peel the potatoes and plunge them into a bowl of iced water. Using the grating blade on a food processor, mash the potatoes and return them to the bowl of ice water. Peel the onion and also grind it using a food processor. Drain the mashed potatoes and let them rest in a colander in the sink for a few minutes.
Press the sides of the colander using a wooden spoon to remove any excess water. Place the chopped onions in a colander and repeat the draining process to remove residual moisture. Finely chop the parsley and chives and proceed.
In a large bowl, combine eggs, salt, garlic cloves, black pepper, and potato starch. Stir the mixture vigorously to ensure thorough mixing. Then add the diced potatoes, onion, half of the parsley, and half of the chives to the bowl, and add them to the mixture.
Carefully remove the hot baking dish from the oven and distribute the oil evenly to coat the bottom and sides of the plate. Transfer the potato mixture to the prepared baking dish, making sure to spread evenly. Place the container in the oven and bake for 45 to 55 minutes.
Once fully baked, garnish the dish with the remaining parsley and chives. Serve immediately.