Cook clams. Chop, saving meat and liquor for chowder.
In large pot melt butter, add fat back and render.
Add celery, onions and sweat. Do not brown.
Add flour. Stir to form roux. Cook 2 minutes.
Add clam liquor, plus 4 cups additional clam juice.
Add clams and potatoes. Cook until chowder thickens and potatoes are soft.
Season with salt pepper and 2 tablespoons fresh thyme.
Add 4 cups heavy cream. Enjoy.
Notes
For true Rhode Island Chowder; add one can crushed tomatoes when adding clams. Proceed as above. Chowder purists (read Bostonians) will see red over that step, in which case, disregard and stick to the original.