In a large pot over medium-high heat, melt butter and add garlic and leeks. Cook for 10 minutes, stirring regularly. Add chicken broth, potatoes, and seasoning. Bring to a boil, cover and reduce heat to medium. Let cook for 20 minutes.
In a saute pan over medium high heat, add oil. Saute sausage until just browned and warmed through.
Remove soup from the heat. Using an immersion blender, blend the soup to a smooth consistency. Stir in heavy cream. Return to medium heat for 5 minutes.
In a shallow soup bowl, ladle soup into center. Place cooked sausage in center of bowl and garnish with parsley, if desired