Cook bacon in heavy large pot over medium heat until crisp. Using slotted spoon, transfer to paper towels to drain. Add leeks to same pot. Cover and cook until leeks are very tender, stirring frequently, about 4 minutes. Add clam juice, potatoes, 1/2 cup water, thyme, and saffron. Bring to boil; reduce heat to medium and cover. Simmer until potatoes are just tender, stirring occasionally, about 7 minutes. Stir in cream and reserved bacon. Season chowder to taste with salt and pepper. Sprinkle cod with salt and pepper; place atop chowder. Cover and cook until cod is opaque in center, about 10 minutes. Using slotted spoon, transfer 1 cod fillet to each of 6 bowls. Ladle chowder over fish and serve.