Heat the bacon fat and butter in a stockpot over medium-high heat. Add the pumpkin and saute for 15 minutes, stirring occasionally. Pour in the stock and simmer, covered, until the pumpkin is very tender, about 30 minutes. Remove from heat. Add the Marsala, thyme, salt, and pepper to taste. Process the soup in batches in a blender until smooth. Return to the stock pot. Add the bacon. Simmer 10 minutes. Serve immediately, garnished with pumpkin seeds.