Heat oil in a large, heavy saucepan over moderate heat. Add onions and cook, stirring occasionally, until soft, about 2 to 3 minutes. Add potato and salt and cook, stirring, another 2 minutes. Add water, cover and simmer until potato is tender, about 15 minutes. Add peas and simmer, uncovered, 2 minutes.
Cool slightly, then purée in small batches in a blender. Force mixture through a very fine mesh sieve into a saucepan. Reheat and season to taste with salt and pepper.
Top each serving with a dab of sour cream and fresh mint leaves.
Nutritional Info Per Serving:
Calories: 86
Fat: 1 g
Protein: 4 g
Carbohydrate: 15 g
Dietary Fiber: 4 g
Sodium: 280 mg
