Combine the butter, peppercorns, honey, and salt to taste in a small bowl. Cover and refrigerate for at least 30 minutes and up to 1 day to allow the flavors to meld. Remove from the refrigerator 15 minutes before serving.
This is the type of soup that, at first glance, might seem a little…unexciting. But you’re underestimating the power of mushrooms, which do the heavy lifting.