1 Melt butter in Dutch oven over medium heat. Add onion, sugar, and 1 teaspoon salt and cook until softened, about 5 minutes. Stir in garlic, ginger, and cayenne and cook until fragrant, about 30 seconds.
2 Add potatoes, broth, water, and ½ teaspoon salt and bring to simmer. Reduce heat to low, cover, and cook until potatoes are tender, 15 to 20 minutes.
3 Working in batches, process soup in blender until smooth, 1 to 2 minutes, then return to pot. Adjust consistency as needed with extra broth. Season with salt and pepper to taste. Serve individual portions with peanuts and cilantro.