1Preheat the oven to 475F. Cover a large baking sheet with heavy-duty foil.
2Using a sharp knife (a serrated blade works well), slice each piece of bread almost in half horizontally. Don’t cut quite all the way through; you want to leave about a 1/2-inch crust “hinge” on each piece, thus creating a flap, or pocket, where you can separate the bread and put the filling.
3To make the filling, in a small bowl place the preserves or marmalade and 1/4 cup of the walnuts and beat briskly with a fork to combine. Spread about 2 tablespoons of the walnut mixture inside each bread pocket, then press down lightly on the filled bread to seal.
4In a pie plate or shallow bowl, stir together the egg product, milk, sugar and cinnamon. Set aside. In a large shallow bowl combine the corn flakes and the remaining 1/4 cup of walnuts. Crush the corn flakes between your fingers until they are broken into tiny, irregular pieces. Dip each slice of filled bread into the egg mixture, turning it three or four times, until the bread is completely coated and has absorbed some of the egg—but don’t let the bread get soggy. Then press each slice, on both sides, into the walnut-corn flake crumbs. Pat the crumbs on if necessary to make them stick, and don’t worry if the coating is not completely even. Continue until all the bread has been dipped and coated, setting the prepared slices aside on a sheet of waxed paper as you work.
5Place the foil-covered baking sheet in the oven to heat for about 3 minutes. Remove from the oven and rapidly coat the foil with nonstick cooking spray, then quickly place the bread in a single layer on the foil. Bake for about 5 minutes, until lightly browned on the bottom. Flip the slices over and bake 3 – 4 minutes longer. Transfer to warmed plates or a platter, dust with powdered sugar and serve with maple syrup, if desired.