Heat the pizza oven to 350°F. Shred potatoes, parsnips and onions in a food processor with the grating attachment. Place a clean kitchen towel over a large bowl. Transfer potatoes and onion into the towel and squeeze out as much moisture as you can into the bowl. Discard the liquid that makes it into the bowl, but don’t rinse it.
Add the squeezed mixture to the bowl. Add the potato starch, baking powder, eggs, dill, chives, salt and pepper and mix well until ingredients are thoroughly combined.
Heat the oil and butter in a 10-inch seasoned cast iron over medium-high heat until the mixture is shimmering. Remove 2 tablespoons of the mixture and transfer to a small ramekin, set aside. You can test the oil by adding a pinch of the latke mixture from the ramekin. If it sizzles upon contact, the skillet is ready. Add the latke mixture to the skillet and pat it firmly into a single even layer. Cook until the bottom is golden brown and crispy, about 10 minutes. Brush the top of the pancake with the reserved butter/oil mixture. Transfer the pancake to the pizza oven and continue cooking until the top is golden brown and the pancake is cooked through, about 10 minutes longer, turning the pan several times (using heavy duty grill gloves). Remove to a cooling rack and let rest for 5 minutes before turning out onto a cutting board.
Sprinkle with a pinch of flaky salt and serve immediately cut into wedges with any of the suggested toppings.
