How to Make It
In a medium saucepan, heat the olive oil. Add the pancetta and cook over moderately high heat, stirring occasionally, until browned and nearly crisp, about 5 minutes. Using a slotted spoon, transfer the pancetta to paper towels to drain.
Add the onion and a generous pinch of salt to the saucepan and cook over moderate heat, stirring occasionally, until the onion is softened and well browned, about 12 minutes. Stir in 1 tablespoon of the flour and cook until a paste forms. Gradually whisk in the milk and bring to a simmer, then cook over moderately low heat, whisking, until thickened and no floury taste remains, 5 to 7 minutes. Scrape the onion béchamel into a medium bowl and stir in the pancetta, parsley, 2 tablespoons of the cheese, 1/2 teaspoon of salt and the crushed red pepper. Let the filling cool completely.
In a large bowl, mix the rice with the beaten egg and the 2 egg yolks until evenly coated. Stir in the remaining 1 cup of pecorino cheese until the rice becomes sticky.
Line a large baking sheet with wax paper. Scoop 3 packed tablespoons of the rice mixture into one moistened hand and press it into a 3 1/2-inch round. Scoop 2 teaspoons of the cooled filling into the center and wrap the rice around it, pressing to form a tight ball. Transfer to the baking sheet. Repeat with the remaining rice mixture and filling to make 12 arancini.
Place the breadcrumbs and the remaining 1 cup of flour in 2 separate shallow bowls. In another shallow bowl, beat the egg whites until frothy. Dust the arancini with flour, tapping off the excess. Roll them in the beaten egg whites and then in the breadcrumbs. Transfer the arancini to the baking sheet and refrigerate, uncovered, until firm, about 1 hour.
In a large saucepan, heat 2 inches of canola oil to 350°. Add half of the arancini to the hot oil and fry over moderate heat, turning occasionally, until golden and heated through, about 4 minutes. Using a slotted spoon, transfer to paper towels to drain. Repeat with the remaining arancini. Pile the arancini on plates or a platter, garnish with chopped mint, grated cheese and coarse sea salt and serve.