1. Cook shallots in oil in a 3-quart heavy saucepan over moderate heat, stirring, until softened, about 2 minutes. Add potato and salt and cook, stirring, 2 minutes. Add water and simmer, covered, until potato is tender, about 15 minutes. Add peas and simmer, uncovered, 2 minutes.
2. Puree in batches in a blender (use caution when blending hot liquids), then force through a very fine sieve into a saucepan. Reheat soup and season with salt and pepper.
3. Drizzle servings with creme fraiche.

Yield: 6 servings