In a large saucepan, bring the chicken stock to a simmer. In a medium saucepan, melt butter over medium heat. Add the onion and saute for 5 minutes or until soft. Add the rice and stir until coated.
Increase the heat to medium-high. Add the wine. Cook, stirring constantly for 4 minutes or until wine is absorbed. Add about 1 cup chicken stock (enough to just cover the rice) and cook, stirring constantly, until the stock is absorbed. Continue adding stock, 1 cup at a time, stirring until it is absorbed before adding more. The rice is done when it is just cooked through and lightly bound with creamy liquid, about 15 minutes.
Remove risotto from heat and stir in Parmesan cheese and scallion. Spread risotto evenly in a greased sheet pan and refrigerate until very firm, at least 4 hours or overnight.
In a large saute pan, heat the olive oil over medium heat. Form risotto cakes by shaping handfuls of risotto into 3 x 1/2 inch disks. Dredge the cakes in flour to coat. Saute cakes in hot oil until golden.