In a medium saucepan, fry onions in oil for about 1 minute. Remove from heat and add split peas and ham hock or bone. Add enough water to cover ingredients, and season with salt and pepper.
Cover, and cook until there are no peas left, just a green liquid, about 2 hours. While it is cooking, check to see if water has evaporated. You may need to add more water as the soup continues to cook.
If you don't want to add a ham hock or bone, you can always use diced ham.
this makes the best soup. My mum taught me to make it this way and it always gets rave reviews, the only thing I do differently is soak the peas overnight changing the water a few times, it helps the pease soften down quicker. I keep my ham bone from xmas in the freezer so it's a cheap alternative, I also add a bacon bone for a bit of smokines. - 20 Jun 2012