Add oil to hot skillet. Brown your sausage just enough where not fully cooked.
Add your potatoes. And then add the water. Mix in your seasonings. The cover and cook over medium heat for about 45 to 60 minutes. Put a fork to your potatoes to make sure they are soft and ready.
About a minute before removing your pan from the heat, take your tablespoon of cornstarch and mix in a small amount of cold water (about a teaspoon size) so that it becomes creamy. Add that to your pan. Cover and allow to boil for one minute. This will thicken your gravy a bit.