Bring a large pot of water to simmer and add the cubed cod. Simmer just until done (this should only take two or three minutes). Add the frozen seafood and simmer just until thawed (about 1 minute). Remove from heat and drain immediately.
Melt the two tablespoons of butter in a Dutch oven or sturdy pot on medium heat. Add the leeks and the mushrooms and cook stirring occasionally until the mushrooms are soft (about 8 minutes). Sprinkle with the 2 tablespoons of flour and cook, stirring for one minute to thoroughly coat the vegetables with flour.
Pour on the white wine and stir well to combine. Then mix in the milk and cream. Heat until thick and just below the boiling point, stirring occasionally. Turn off the heat and add the parsley, cayenne, and salt and pepper to taste. Stir in the seafood mixture.
Pour the mix into a 9X13 inch buttered baking dish. Mix together the parmesan cheese and the bread crumbs and sprinkle this evenly on top of the casserole.
Bake for 20 minutes at 350°F. Serve your seafood casserole piping hot with rice.