Start by heating up a small pot of vegetable broth to have ready. You'll want this warm and simmering nearby on the stove as you cook the risotto. You can make your own or use a brand you trust, just be sure that it's seasoned well as the risotto is only salted with the broth.

While the broth heats up, toast the rice in a skillet over medium/high heat. Do so for just a minute or two, tossing or stirring it frequently to prevent burning. Set aside.

Add the olive oil and diced onion into a saucepan over medium heat. Sauté the onion until it is tender and slightly transparent, then add the rice into the pot. Stir so that the olive oil can be absorbed a bit by the rice, then add the white wine and bring to a simmer.

Once the excess moisture has burned off and the smell of alcohol is gone, add 1-2 ladlefuls of warm broth into the rice, along with the tomato sauce. Keep the rice submerged in just enough liquid to cover, and simmer until it is al dente to your taste (check the package for specific cook time recommendations). Continue to ladle in more broth as necessary to maintain moisture in the pot.

When the rice is cooked to your taste, take the risotto off the heat and stir in the butter and cheese. Cover the pot and let it rest for 2-3 minutes before serving.