In a medium skillet over medium-low heat, sauté onions, celery and garlic in olive oil until onions are translucent - do not brown the onions. Set aside.
START THE CHOWDER
In a large dutch oven or soup pot, bring clams, clam juice and potatoes to a boil. Immediately reduce to a simmer and add sautéed onion mixture to pot.
MAKE THE ROUX MIXTURE
In the skillet, melt the butter over medium heat. When the butter stops bubbling, slowly add the flour while whisking. Turn heat to low and whisk/stir to fully incorporate without trying to brown the roux - about 30 seconds as this is a blonde roux. Turn the heat off and whisk in the cream until smooth and well incorporated.
FINISH THE CHOWDER
Add all of the roux mixture to the soup pot and stir to incorporate. Add salt and pepper (you can add more later if needed) and simmer for about 15 minutes. Taste and re-season with additional salt and pepper, then serve in bowls with warm French, Italian or sourdough bread.
Garnish with parsley, more pepper, homemade croutons, green onions, chives, hot sauce, or whatever else you desire.
Notes
Instead of frozen clams, you can use equal amounts of canned clams (which are precooked) with their juices. If using canned clams, omit the salt in this recipe and just add salt to taste at the end.We purposely add less salt than we prefer to this soup and have salt and pepper on the table so people can salt to their liking, but extra finishing salt is recommended for this clam chowder.