In a large stockpot over medium heat, crisp the pancetta in half of the butter and half of the olive oil for 5-6 minutes.
Add the remaining butter, olive oil, celery and shallots and cook for 3-4 minutes.
Add the flour and blend well, cooking until flour turns pale beige, about 2 minutes.
Add clam juice and bring to a boil.
Allow chowder to reduce and thicken for a few minutes.
Add potatoes and simmer over low heat until tender, about 15 minutes.
Add chopped clams and scallops and simmer, about 3 minutes.
To finish, add milk, parsley, thyme and pepper. Return to a simmer briefly.
Check for seasoning. Ladle into cazuela soup bowls and add a fine drizzle of Tuscan Herb oil. Serve with crusty bread.