Prepare the cooker indirect at 275° F.
In a Dutch oven over medium heat, melt the butter with the oil. Add the leeks and cook for 2 minutes. Add the potatoes and cook for about 5 minutes, stirring occasionally. Add the sausage and garlic and cook about another 5 minutes, or until everything is getting soft. Add all the other ingredients and bring to a boil. Reduce to a simmer and cook for 20 minutes.
Pour the soup into the pumpkin. Replace the top on the pumpkin and place it in the cooker. Cook for about an hour, but watch it so the pumpkin doesn't get too soft and collapse. When the pumpkin feels tender, carefully remove it to a pie pan or quiche dish. Stir and then serve. Scrape some of the pumpkin away from the sides to serve with the soup.