For the Potage:
Heat the olive oil over medium heat in a Dutch oven or 6 quart pot. Add onion and cook 2 minutes . Add garlic and continue cooking until vegetables are translucent and fragrant, approximately 5 minutes.
Add mushrooms and stock and simmer for 15 minutes. Purée the mixture using a stick blender until smooth.
Stir in the lemon juice, cream, thyme, rosemary and parsley and simmer for an additional 10 minutes. Serve in pre-heated bowls.
For the Roasted Mushrooms:
Preheat oven to 375°F. In a large bowl, mix the mushrooms, olive oil, thyme, pepper and salt until blended. Arrange in a single layer on a sheet tray.
Roast the mushrooms, stirring halfway through, for 20 to 25 minutes, and mushrooms liquid has evaporated. The mushrooms are done when they are aromatic and brown around the edges.