1. Heat oven to 450°F. Spray 13x9-inch glass or ceramic baking dish with cooking spray. Heat 1/4 cup of the oil in large skillet over medium heat until hot. Add onions; stir until coated with oil. Cover and cook 5 minutes or until onions are wilted and almost tender.
2. Uncover; cook 10 to 15 minutes or until rich golden brown, stirring frequently and reducing heat to medium-low if necessary. Stir in garlic; cook 1 minute.
3. Whisk eggs and egg yolks in large bowl until blended. Whisk in potato starch, remaining 1/4 cup oil, salt and pepper.
4. Peel potatoes and shred using shredding blade on food processor or box grater; squeeze with hands to remove any excess moisture. Stir into egg mixture. Stir in carrots, parsley and onion mixture until thoroughly combined. Pour in boiling water; stir quickly to combine. Spoon into baking dish.
5. Bake 25 minutes. Reduce oven temperature to 375°F.; bake an additional 30 minutes or until golden brown on top.