Meanwhile, heat 2 tablespoons butter in a Dutch oven over medium-high heat. When foaming subsides, add diced onion and ½ teaspoon of salt. Stir occasionally until softened. Add arborio or carnaroli rice and stir until rice is completely coated in butter, turns translucent, and gives off a roasted, starchy aroma. Add wine and bring to a boil. Lower heat to medium, and begin to add warm whey one ladleful at a time. Stir often, but not constantly. When all liquid is absorbed, add another ladle or two of whey and stir. Continue stirring in liquid until rice is plump and creamy. Remove from heat, and butter and a few tablespoons of freshly grated cheese.