Bring stock to a simmer in a large saucepan. Keep warm over low heat, but do not boil.
Heat a Dutch oven over medium heat. Add oil to the pot; swirl to coat. (Everything from here on will be added to this pot.)
Add onion; cook 5 minutes, stirring occasionally.
Add the Arborio rice and salt, cook 1 minute, stirring frequently.
Add ½ cup stock; cook 2 minutes or until liquid is absorbed, stirring frequently.
Stir in 1 ½ cups stock; cook 4 minutes or until liquid is nearly absorbed, stirring constantly.
Add remaining stock, ¾ cup at a time, stirring nearly constantly until each portion is absorbed before adding the next (about 20-25 minutes); reserve ⅓ cup stock at last addition.
Remove pot from heat.
Stir in reserved remaining stock, butter, pepper, and cheese.
Top the risotto with parsley.
