Place 2 teaspoons oil in large stock pot and saut garlic, onions and celery for 6 to 8 minutes. Slice mushrooms Add mushrooms, reserving one cup (until the end). Add potatoes to pot and continue to saut for an additional 5 minutes. Add the stock and bring to a slow boil. Reduce heat and simmer on medium-high heat until the potatoes are tender when pierced with a fork. Remove from heat and add thyme. Puree in blender, return to pot. Add sherry, half and half, salt, pepper and Worcestershire sauce, warm through. Meanwhile, saute the reserved mushrooms in one teaspoon oil, and season them with salt and pepper. Add to the pot. Serve warm.