Made only in Greece, Graviera is a hard sheeps-milk cheese that becomes creamy when cooked. Its subtle sweetness and luxurious texture make this risotto stand out, but you can substitute Parmesan in a pinch.
Bring stock to a boil in a medium saucepan. Remove from heat.
Heat oil in a medium saucepan over medium heat. Add onion, and cook until translucent, 5 to 6 minutes. Add rice, and stir to coat with oil. Add wine, and cook, stirring frequently, until wine has been completely absorbed, about 2 minutes.
Add 1/2 cup of the hot stock, and cook, stirring constantly, until the stock has been completely absorbed and a wooden spoon drawn through rice leaves a trail. Continue stirring and adding stock, 1/2 cup at a time, waiting for each addition to be absorbed before adding the next, until you've added all but 1/4 cup of the stock. Rice will be just cooked through and still slightly firm in the center. (It should take 20 to 25 minutes.)
Stir in the peas, and cook until they are warmed through and risotto is creamy, about 5 minutes.
Remove from heat. Stir in cheese, parsley, dill, oregano, lemon zest and juice, butter, and remaining 1/4 cup stock. Season with pepper. Sprinkle with cheese, and garnish with dill sprigs.