Directions

1. In a large saucepan, heat oil over medium. Add onion, potatoes, and fennel; season with salt and pepper. Cook, stirring frequently, until onion has softened, about 10 minutes (do not allow vegetables to brown).
2. Add wine, increase heat to medium-high, and cook until liquid has nearly evaporated, 5 to 7 minutes.
3. Add clam juice and 3 cups water. Bring to a boil, then reduce to a simmer; cook until potatoes are tender, 10 to 12 minutes.
4. In a small bowl, whisk egg yolks. Whisking constantly, gradually ladle about 1 cup of hot liquid from saucepan into yolks; add mixture to pan. Add fish, and simmer gently until fish is opaque and soup is slightly thickened (do not boil), 4 to 5 minutes. Season with salt and pepper.
5. Ladle soup into serving bowls; garnish with fennel fronds, if desired. Spread toasted bread with Lemon Aïoli, and serve alongside soup.