1 ounce dried porcini mushrooms
2 cups boiling water
1 tablespoon butter
1/2 onion, diced
1 1/4 cups sliced cremini mushrooms
4 cloves garlic, minced
1 sprig fresh thyme
1 1/2 cups heavy cream
1 teaspoon salt
1/4 teaspoon black pepper
Rinse the porcini mushrooms well, then place in a heat-safe bowl, and cover with the boiling water. Set aside to soak.
Meanwhile, heat the butter in a Dutch oven over medium heat. Add the onion and the mushrooms. Season with a pinch of salt, and cook, stirring occasionally, until the vegetables have reduced and caramelized, about 20 minutes.
Add the garlic, and sauté until fragrant -- about 1 minute -- then add the soaked porcini mushrooms, the soaking liquid and the sprig of thyme.
Bring to a boil, then reduce to a simmer and cook for about 15 minutes, stirring occasionally.
Remove the thyme, and season the soup with black pepper. Remove the soup from the heat, and add the heavy cream. Use an immersion blender to blend the soup until quite smooth.
Return to the heat just long enough to heat the soup through. Season with salt to taste and serve.