Melt butter in a large pot of medium heat. Add onions and sauteed until tender, stirring often, about 5 minutes. Add garlic and sauteed 1 minute more.

Add vegetable stock, all clam juice (including reserved juice from can of clams), tomatoes, amd tomato sauce, salt, pepper, and red pepper flakes. I also add 1/4 tsp baking soda at this point to neutralize the acidity of the tomatoes. Careful, it will foam which is a natural reaction. Bring to a boil, reduce heat to medium low, cover and simmer for 15 minutes.

At 15 minutes add cod pieces. Simmer 5 minutes. You may need to increase the heat again to come back to a simmer quickly.

After 5 minutes add entire bag of seafood mix. Simmer 5 minutes more. Remove from heat and stir in baby clams to heat through. Taste for seasoning and adjust as needed.