Step 1

The broth can be made ahead, covered, and chilled. Put some of the broth on the shellfish to keep them from drying out.

Step 2

Heat butter and oil in a large pot over medium heat. Add onion and garlic. Cook, stirring occasionally, until softened, 6-8 minutes.

Step 3

Stir in the parsley; season with salt and pepper. Add the wine and bring the mixture to a boil. Reduce the heat and simmer about 4 minutes.

Step 4

Add clams, mussels, and 4 cups of water. Cover and bring to a boil. Reduce heat and simmer until the shellfish open, 7-9 minutes. Strain stock through a large fine-mesh sieve into a large measuring cup or bowl. Discard any mussels or clams that do not open.

Step 5

Let the shellfish cool so you can handle them. Remove the meat from the shellfish, cover with some broth and set aside.

Step 6

Heat 3 Tablespoons olive oil in a large heavy pot over medium heat. Add onion, leeks, celery, garlic, and parsley; season with salt and pepper. Cook until the vegetables are sort, but have taken on no color, 15-20 minutes, stirring occasionally and reducing heat if needed to keep them from browning.

Step 7

Add potatoes and cook for 10-15 minutes more until the potatoes just begin to soften.

Step 8

Just before the vegetables are done, melt the butter in a large saucepan over low heat. Whisk in the flour and cook, whisking often, until the roux just begins to smell nutty, about 2 minutes. Add the cream and milk, whisking until smooth. Bring to a simmer and cook until the bechamel is just thickening, about 1 minute.

Step 9

Add bechamel along with reserved broth to the vegetables. Bring to a simmer and cook for 20-30 minutes. Season with salt and pepper.

Step 10

Coarsely chop half of the shellfish meat and add it to the chowder along with the remaining shellfish meat. Stir in half of the smoked salmon and cook until it has warmed through, about 1 minute.

Step 11

Serve the chowder with the remaining smoked salmon, a bit of dill, and a few grinds of pepper.