In a large saucepan add butter and chopped onion and sauteacute; over medium heat until the onion turns soft and translucent. Add Arborio rice, cook over medium heat, stirring constantly, for about 3 minutes, or until opaque. Do not brown or burn the rice.
Add 1 cup of warm broth to the pan, stirring constantly and scraping the bottom of the pan so it doesn't stick. Also scrape the sides to get all the uncooked rice mixed in. You want to see bubbles in the liquid to know it is absorbing, but if it is bubbling too much the rice may stick to the pan and burn. Turn down the heat slightly to simmer.
Once the broth is almost absorbed add in another cup. You need to pay attention and stir it often, but at this point you don't need to stir it constantly. Just keep an eye on it to make sure it doesn't burn. Repeat these steps until all the broth is absorbed and the rice is creamy. It should take about 20-25 minutes.
Taste the rice to make sure it is done. It should be tender, but not mushy, almost like thick oatmeal. If it is still crunchy, add broth in 1/4 cup increments and cook until it reaches the desired doneness. If you run out of broth, use warm water.
Add salt and pepper to taste.