In a pot, melt the butter over low heat. Add onion and melt for about 3 minutes. Add peeled and diced sweet potatoes and cumin. Continue to sauté for 2 minutes.
Add broth and bring to a boil.
Reduce heat and simmer, covered, for 8 to 10 minutes until potatoes are tender. Mix with a food processor.
Meanwhile, cook your lentils in a pan of cold water (3 times their volume) for about 25 to 30 minutes.
Drain. Stir lentils into sweet potato soup and cook over medium heat for 5 minutes or until heated through.
Remove from heat and stir in cubed Gouda cheese. Add salt and pepper to taste. Ladle the soup into bowls and enjoy.