Fish Soup with Lemon Aioli

Name: Fish Soup with Lemon Aioli
Ingredients: 2 tablespoons olive oil; 1 small onion, finely chopped; 2 baking potatoes, (8 ounces each), peeled and cut into 1/2-inch cubes; 1 small bulb fennel, (about 10 ounces with stalks), trimmed, halved lengthwise, cored, and cut into 1/2-inch dice, fronds reserved for garnish (optional); Coarse salt and ground pepper; 1 cup dry white wine; 1 bottle (8 ounces) clam juice; 4 large egg yolks; 1 pound skinless cod fillet, or other white fish, cut into 1 1/2-inch chunks; 4 thick slices crusty bread, lightly toasted, for serving; Lemon Aioli, for serving