In small saucepan, cook onion in butter over moderately low heat, stirring 5 minutes. Mix in 1/4 cup flour, and cook, stirring constantly, 3 to 4 minutes. Stir in milk and bouillon. Cook mixture, stirring until it forms a paste. Continue to stir and cook paste 3 minutes. Remove pan from heat, stir in turkey, potatoes, paprika, salt, pepper and parsley. Combine mixture well.
Chill turkey mixture, covered, 2 hours or until firm. Divide into 8 portions; roll or mold into desired shape. Dredge balls in additional 1/2 cup flour, shaking off excess. Coat balls thoroughly with egg wash, letting excess drip off; then dredge in bread crumbs. Transfer croquettes to parchment paper. Allow them to dry at room temperature for 30 minutes before frying.
In large saucepan, heat 2 inches of oil until deep-fat thermometer registers 365°F. Fry croquettes in batches 3 to 4 minutes, or until golden brown. Transfer to paper towels to drain.