Step 1

Prepare an ice-water bath. Bring a pot of water to a boil. Score an X into the bottom of each tomato using a sharp paring knife. Blanch tomatoes until skins loosen, 30 seconds to 1 minute. Transfer to ice-water bath using a slotted spoon. Peel and discard skins. Core and coarsely chop tomatoes.

Step 2

Heat 1 tablespoon oil in a medium Dutch oven or a large pot over medium-high heat. Cook onion, garlic, and sliced fennel until fragrant and softened, 3 to 5 minutes. Season with 1/2 teaspoon salt and 1/4 teaspoon white pepper. Remove from heat, and add wine. Return to heat, and bring to a boil, scraping up brown bits from bottom using a wooden spoon. Cook until reduced by half, about 2 minutes.

Step 3

Add stock and chopped tomatoes. Bring to a simmer. Stir in cod and shrimp, and return to a simmer. Remove from heat, and let stand, stirring halfway through, until cod and shrimp are just cooked through, about 3 minutes. Divide soup among 4 bowls, and drizzle with remaining tablespoon oil. Garnish with reserved fennel fronds. Serve immediately.