How to Make It
Melt the butter in a large saucepan. Add the onion, fennel and celery root and cook over moderate heat, stirring occasionally, until crisp-tender, about 10 minutes. Add the salmon and cook, stirring, for 1 minute. Add the wine and cook over high heat until reduced to 1/3 cup, 7 to 8 minutes. Add the fish stock and bring to a boil. Cover, reduce the heat to moderately low and simmer until the vegetables are tender, about 15 minutes.
Strain the broth into a bowl. Working in batches, puree the solids in a blender, adding just enough of the broth to make a smooth puree. Return the puree and the remaining broth to a clean saucepan. Stir in the cream and season with salt and pepper. Simmer over low heat for 5 minutes. Ladle the bisque into bowls and serve with lemon wedges.