In medium saucepan, bring 1 cup water and salt to a boil. Stir in wild rice and return to a boil. Reduce heat to low, cover and simmer until tender, about 55 minutes. Drain and set aside.
Meanwhile, in large saucepan, heat oil over medium-high heat. Add garlic, onion and thyme and cook, stirring often, 2 minutes. Add mushrooms, reduce heat to medium and cook, stirring occasionally, until onion is tender, about 7 minutes. Add broth and bring to a boil. Reduce heat to low, cover and simmer 20 minutes.
Transfer half of soup to blender and blend until almost pureed. Return to saucepan and stir in wild rice and pepper. Return to a simmer over medium-high heat. Cover, reduce heat to low and simmer 10 minutes. Adjust seasoning to taste. Just before serving, stir in sherry if desired.