Combine lime juice, garlic, and salt to taste in large bowl. Place fish in juice, turn to coat well and let sit 10 minutes. Remove, pat dry and set aside.
Put 1 cup fish stock in blender with tomatillos, jalapeños, cilantro, epazote and 5 hoja santa leaves. Process until smooth and set aside.
Heat butter over medium heat in Dutch oven or large saucepan until foamy. Add puréed sauce and cook 3 minutes, stirring occasionally. Add remaining 3 cups stock and bring to boil over high heat, then lower heat and simmer 5 minutes. Add fish fillets and cook until just firm to the touch, 4 minutes.
Purée remaining 1 hoja santa leaf with some stock or water in blender or food processor, add to pot and bring back to boil. Transfer fish fillets to large soup bowls and add 1 cup stock to each.
