Sweet Potato and Sausage Soup

Source: Diana's Kitchen

1/2 pound Spicy sausage ( Andouille ) 
1/2 Stick butter 
1 1/4 cups Chopped onion 
1 teaspoon Thyme 
1 1/2 pounds Sweet potatoes -- peeled 
And cubed into 1/2 pieces 
1/4 cup Praline liqueur 
7 cups Chicken stock 
1/2 cup Brown sugar 
1/4 cup Plus 2 Tbs heavy cream 

Cook diced sausage in skillet with 2 tbs butter for 5 minutes. Add onion and cook until soft. Add thyme and sweet potatoes and cook 5 minutes. Add liqueur and broth and cover and simmer over low heat for 45 minutes or until potatoes tender. In blender puree soup in batches. Return to pan and stir in cream and remaining 2 tbs butter. Warm but do not boil.