To prepare the gastrique, in a large saucepan, combine the wine, sugar, bay leaves, peppercorns and thyme, stirring to dissolve the sugar. Bring to a boil, reduce to a simmer and simmer until the mixture has reduced to 1 cup. Strain and set aside.  

To prepare the mushroom stock, on a baking sheet, toss the mushroom stems with 2 tablespoons of the olive oil and season with salt and pepper. Roast until lightly browned, 15 to 30 minutes. Reserve any juices. 

In a 2-quart saucepan, combine the roasted mushroom stems, half of the onion, 3 of the garlic cloves, the water and the peppercorns. Bring to a boil, reduce the heat and simmer for 1 hour. Strain and reserve the mushroom stock for the soup.

Preheat the oven to 425°F. 

To prepare the mushroom velouté, on a baking sheet, toss the mushroom caps with the remaining 2 tablespoons olive oil and season with salt and pepper. Roast until very soft, 15 to 30 minutes, depending on size. Reserve any juices.

In a large, heavy pot over medium heat, melt the butter. Add the remaining onions, garlic and thyme and cook, stirring constantly, until the onions are soft and translucent, 7 to 10 minutes. Add the roasted mushroom caps, mushroom stock, reserved roasting juices and bay leaves and bring to a boil. Reduce the heat and simmer, stirring occasionally, for 1 hour. Remove and discard the bay leaves. Add the cream and return the soup to a simmer.

Working in small batches, puree the soup in a blender. Adjust the seasoning with salt and pepper. For a smoother consistency, strain the soup through a fine-mesh sieve before serving.

Ladle the soup into bowls, drizzle with the black pepper–Zinfandel gastrique and serve.