Melt butter in a soup pot over low heat.

Cook chopped onion in butter until soft (10-13 mins).

Add minced garlic, sliced ginger, and cardamom, cook for 1 min.

Increase heat, add jalapeno, cubed sweet potatoes, 4 cups broth, and salt.

Bring to a boil, then reduce heat to low, cover, and simmer until potatoes are soft (15-20 mins).

Puree the soup in batches using a blender until smooth.

Return pureed soup to the pot.

Add remaining broth and heavy cream (optional), simmer over low heat.

Add lime juice and brown sugar, season with salt and white pepper.

Combine yogurt, diced apple, chopped mint, and minced jalapeno in a bowl.

Season raita with salt and pepper.

Refrigerate raita until serving.

Ladle soup into bowls and top with raita.