Bring stock to a simmer in a saucepan over medium. Reduce heat and keep warm. Melt the butter and heat the oil in a large skillet or wide-bottomed pot. Add the rice; stir to coat all the grains, 1 minute.  Add 1 ladle of broth (½ cup to ¾ cup), stir, and leave it alone until broth is nearly absorbed, 2 to 3 minutes. (Run a wooden spoon through it; rice should slowly fill in the channel.)  Stir, add another ladle of broth, and stir again. Cook undisturbed until the broth is absorbed, 3 minutes. Repeat until about 1 ladle of broth remains, 15 to 18 minutes of total cook time for the rice. Turn off heat.  Add salt, remaining broth, and cheese. Stir gently for 2 minutes. Serve immediately in warmed bowls, with more grated cheese over top, if desired.