Instructions: Melt oil and butter in a large heavy pot over moderately low heat. Add garlic and cook, stirring occasionally, until golden brown and caramelized, 10 to 12 minutes. Add onions and shallots and cook, stirring frequently, until onions are softened, about 10 minutes.

Stir in potato, vinegar, and rosemary. Increase heat to high and saute, stirring, for 2 minutes. Add broth and bring to a boil, then simmer, uncovered, until vegetables are very soft, 20 to 25 minutes.

Puree soup in 3 batches in blender (use caution when blending hot liquids) until very smooth. Stir in cream and buttermilk and season with salt and white pepper. Serve hot.

Cooks note:
o Soup can be made (without cream and buttermilk) 2 days ahead and chilled, covered. Do not bring to a boil once buttermilk has been added.

Serves 8 to 10 as a first course (10 cups)

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