Heat oil to 375 degrees F in a deep saucepan.
Season sole fillets with salt and pepper. Dredge fillets in seasoned flour and fry in hot oil until golden brown. Remove and drain on paper towels.
In a 12 to 14-inch saute pan, heat extra virgin oil over medium heat. Add onions and cook until softened and just light brown, 10 to 12 minutes. Add currants, sugar, pine nuts and vinegar and bring to boil. Cook 5 to 6 minutes until currants are soft and allow to cool. When all ingredients are cool, choose an earthenware dish that just fits the fried fillets, slightly overlapping. Top with sweet and sour mixture and refrigerate for 24 hours. Serve at room temperature.
Recipe Courtesy of Mario Batali