Put 5 cups of water in a large pot over high heat. Cover and bring to a boil.
While the water heats, peel the carrots and chop them into 1-inch cubes. Add them to
the water (even before it boils) as you chop them. Repeat with the potatoes. Stem
the pepper, remove its seeds and mince it. Add to the pot along with salt and pepper.
When the water boils, lower the heat and simmer 30 minutes. The potatoes should
Use a slotted spoon to transfer the potatoes to a blender and blend until smooth,
adding the cooking liquid as you blend. Reheat the soup. (Fill the blender with
soap and warm water and blend it to clean it.)
If you like the soup extra smooth, put it through a fine-mesh sieve.
Serve in warm bowls topped with sour cream, if desired.