Do not even think about using canned chopped clams or bottled clam juice. Go for live clams.

What you need, for four person
A dozen of clams, cherry stone is preferred.
White wine 4 tbs
Bacon 4-5 slices, chopped
Onion, chopped 1/2 cup
Butter 1tbs
Flour 1-2 tbs
Potato 1 cup, diced
A　bay leaf
Milk about 2 cups
Salt and pepper
Finely chopped parsley for garnishing

What to do

Most clam chowder recipe starts by chopping the clam. But I would first steam them with a little bit of white wine to obtain more flavorful juice.  The meat of clams will be more plump as well.

1) Wash the clams with cold running water and put them in one layer in a pot or pan which can be covered tightly.

2) Sprinkle wine over the clam and cover. Heat for 3-4 min over high heat to open the shells. Do not overcook. Set aside till the clams get a little colder.

3) With using a table knife, take the clam meat from the shell.

4) Strain the juice in the pot through a sheet of kitchen paper and set aside.

5) In a soup pot, melt butter over medium heat and saute chopped onion for 2 min.

6) Add the chopped bacon and a bay leaf, keep sauteing until onion gets tender.

7) Sprinkle flour and mix well. It’s getting sticky in the pot so quickly add small amount of milk (about 3-4 tbs) and mix well.

8) Gradually add 1 cup of milk, mix well each time you add.

It should be thick and creamy. Set aside the remaining milk to add later.

9) Add the clam juice and diced potato. Heat over medium- low heat until potato gets tender, about 15-20 min.

10) Chop the clams and add into the pot when the potato is tender.

11) Add remaining milk until desired thickness.  You can also use half & half or heavy cream for richer, creamier finish.

Add salt and pepper to taste, sprinkle chopped parsley and enjoy!

I have the recipe in Japanese, too.
ニューイングランド風クラムチャウダー