Preparation Generously cover potatoes with salted cold water (2 teaspoon for 4 quarts) in a large pot, then simmer until tender, about 15 minutes. Drain potatoes and chill in a large bowl until cool, about 45 minutes. Mash potatoes, then stir in cheeses, onion salt, parsley, 1/2 teaspoon pepper, and salt to taste. Stir in 1 egg. Form potato mixture into 24 oblong croquettes (about a scant 1/4 cup each). Lightly beat remaining 2 eggs in a shallow bowl and put bread crumbs in another shallow bowl. Dip 1 croquette into egg, letting excess drip off, then roll in bread crumbs to coat. Transfer to a parchment-paper-lined baking sheet. Repeat with remaining croquettes. Heat 1/2 inch oil in a 12-inch heavy skillet over medium-high heat until it shimmers. Fry croquettes in batches, turning occasionally, until golden brown, 4 to 5 minutes per batch. Transfer to paper towels to drain. Serve immediately.
Preparation Generously cover potatoes with salted cold water (2 teaspoon for 4 quarts) in a large pot, then simmer until tender, about 15 minutes. Drain potatoes and chill in a large bowl until cool, about 45 minutes. Mash potatoes, then stir in cheeses, onion salt, parsley, 1/2 teaspoon pepper, and salt to taste. Stir in 1 egg. Form potato mixture into 24 oblong croquettes (about a scant 1/4 cup each). Lightly beat remaining 2 eggs in a shallow bowl and put bread crumbs in another shallow bowl. Dip 1 croquette into egg, letting excess drip off, then roll in bread crumbs to coat. Transfer to a parchment-paper-lined baking sheet. Repeat with remaining croquettes. Heat 1/2 inch oil in a 12-inch heavy skillet over medium-high heat until it shimmers. Fry croquettes in batches, turning occasionally, until golden brown, 4 to 5 minutes per batch. Transfer to paper towels to drain. Serve immediately.