- 1small onion, unpeeled, quartered
- 2stalks celery, chopped
- 1leek, dark green parts chopped, rinsed, white parts cut into ¼” rounds, rinsed, reserved for stew
- 12 c fish stock
- ½ tsp. crushed red pepper flakes
- 1garlic clove, smashed
- 6thyme sprigs
- 2bay leaves (optional)
- ½cup dry white wine or sake
- 1lb. small Yukon Gold potatoes, quartered
- Kosher salt
- 1fennel bulb, halved lengthwise, thinly sliced crosswise, fronds reserved for serving
- 1 ½lb. boneless, skinless white fish (such as cod), cut into 1″ pieces
- 2cups Sun Gold tomatoes
- Extra-virgin olive oil (for drizzling)
- Freshly ground black pepper
Heat oil in a large pot over medium. Add onion, celery, dark green leek pieces, chile, garlic, thyme, and bay leaves (if using). Cook, stirring occasionally and scraping bottom of pot to make sure nothing is sticking, until onion is golden brown, 4–6 minutes. Add wine and cook, stirring occasionally, until reduced by about half, about 1 minute.
Add fennel seeds and 12 cups cold water to onion mixture and bring to boil. Reduce heat to medium-low, bring to a simmer, and cook, skimming off any foam that rises to the top, until stock is nicely flavored 40–50 minutes. Let cool 30 minutes. Strain through a fine-mesh sieve into another large pot or bowl; discard solids.
Place potatoes in fish stock in a large pot, season with salt, and bring to a boil. Reduce heat to medium, bring to a simmer, and cook, stirring occasionally, until potatoes are almost tender, 10–14 minutes. Add sliced fennel and white leek parts and cook, stirring occasionally, until vegetables are barely tender, 4–6 minutes. Add fish and cook, stirring occasionally, until fish is opaque, about 4 minutes. Remove from heat and stir in tomatoes; taste and adjust seasoning.
Ladle chowder among bowls and top with fennel fronds. Drizzle with oil; season with pepper.