How to Make It
In a large pot, melt the butter over moderately low heat. Add the celery, the chopped scallion bulbs, and the garlic and cook, stirring occasionally, until the vegetables start to soften, about 10 minutes.
Add the potatoes, wine, water, broth, thyme, bay leaf, and salt to the pot. Bring to a boil. Reduce the heat and simmer, partially covered, until the potatoes are tender, about 15 minutes.
Stir the half-and-half into the soup. Simmer until the soup starts to thicken, 2 to 3 minutes. Remove the pot from the heat and stir in the trout and the scallion tops. Remove the bay leaf from the soup.
If peppered smoked trout isn't available, use regular smoked trout and one teaspoon fresh-ground black pepper instead.