1. In a medium saucepan, bring the chicken stock to a simmer over moderate heat. Butter a 9 by 13 inch glass baking dish.

2. Melt 4 tbsp of the butter in a large non-reactive saucepan. Add the onion and cook over moderate heat, stirring occasionally, until softened, about 5 minutes. Add the rice and stir until coated with butter, 1 to 2 minutes. Raise the heat to moderately high and pour in the wine. Cook, stirring, until almost all the wine is absorbed, about 4 minutes.

3. Add about 1 cup of the simmering stock ( enough to just cover the rice ) and cook, stirring constantly, until the stock is absorbed. Continue adding stock, about 1 cup at a time; stir constantly until the stock is absorbed before adding more. The rice is done when it is just cooked through and lightly bound with with creamy liquid, after about 15 minutes. Remove from the heat and stir in the Parmesan cheese. Let cool slightly, then stir in the egg. Spread the risotto evenly in the prepared baking dish. Cover and refrigerate until very firm, at least 4 hours or overnight.

4. Cut the risotto into 16 even squares. Shape each square into a disk, about 2 1/2" in diameter and 1/2" thick. Coat the disks with flour and refrigerate on a baking sheet until firm, about 20 minutes.

5. In a skillet, melt 1 tbsp of the butter in 1 tbsp of the olive oil. Add 8 of the cakes to the skillet and cook over moderately high heat, turning once, until browned and warmed through, about 3 minutes per side. Transfer the cakes to a warm serving platter, cover and keep warm in a low oven. Wipe out the pan and repeat with the remaining butter, oil, and risotto cakes. (The risotto cakes can be fried up to 1 day ahead. To serve, warm them in a 450 degree oven for about 10 minutes, or until heated through.)