Melt the butter in a dutch oven

Add the onion and saute until soft, stirring often

Stir in the flour to make a roux, cook for a minute or two on medium heat, stirring constantly
Add the chicken stock slowly whisking while you add it 

Add the cream, bay leaves and potatoes

Bring to a simmer, then cook on low heat until potatoes are soft, about 20 minutes

Add clams with juice, salt and pepper

Let simmer for about 5 minutes to heat clams