In a dutch oven or large pot, melt the butter.  Add the onions, carrots, and leeks.  Cook for about 5 minutes, stirring often to soften the vegetables.

Add the potatos and cook for a few more minutes, stirring often.  Add the flour, continuing to stir, and cook for a few more minutes.  Add the chicken stock, saffron, pepper, salt, thyme, and bay leaves.  Stir until the chowder is well blended.

Bring the chowder to a boil, then turn it down to a nice medium simmer and cook for about 40 minutes.  Stir it often to make sure nothing is sticking to the bottom of the pot.  Taste for seasoning.  Remove bay leaves and thyme, if you left the leaves on stem.

In a separate pot, add the cream and heat it until a wrinkled film forms over the top.  Turn off the heat under the chowder and add the cream; stir it in thoroughly.  

At this point, you can leave the chowder chunky, or remove 1 cup of the chowder (set aside),  and puree the remaining soup, using a hand-held puree machine, then add back the cup of chowder.  Or puree the soup completely.  Your choice.

Serve the chowder with a slice of French Brie cheese on top.