Preparation Heat 3 tablespoons oil in heavy large skillet over medium heat. Add onions; sauté until golden, about 15 minutes. Meanwhile, cook potatoes in large pot of boiling salted water until tender, about 45 minutes. Drain. Peel hot potatoes; place in bowl. Mash potatoes well. Cool to lukewarm. Mix in parsley, eggs, salt, pepper and onions. Cool completely. Place flour in dish. Using 1/4 cup potato mixture for each croquette, shape into 1/2-inch-thick patties. Lightly coat each with flour. Place on baking sheet. (Can be made 8 hours ahead. Cover; chill.) Preheat oven to 300°F. Pour additional oil into large skillet to depth of 1/4 inch; heat over medium-high heat. Fry croquettes in batches until golden, about 4 minutes per side. Keep warm in oven.
Preparation Heat 3 tablespoons oil in heavy large skillet over medium heat. Add onions; sauté until golden, about 15 minutes. Meanwhile, cook potatoes in large pot of boiling salted water until tender, about 45 minutes. Drain. Peel hot potatoes; place in bowl. Mash potatoes well. Cool to lukewarm. Mix in parsley, eggs, salt, pepper and onions. Cool completely. Place flour in dish. Using 1/4 cup potato mixture for each croquette, shape into 1/2-inch-thick patties. Lightly coat each with flour. Place on baking sheet. (Can be made 8 hours ahead. Cover; chill.) Preheat oven to 300°F. Pour additional oil into large skillet to depth of 1/4 inch; heat over medium-high heat. Fry croquettes in batches until golden, about 4 minutes per side. Keep warm in oven.