First, remove any small bones, pieces of cartilage, or skin from crab and salmon.
Transfer clean meat to a medium bowl and shred into small pieces with a fork (or your fingers). Add the soft bread crumbs, green onion, parsley, salt, pepper, and old bay seasoning to the salmon and crab and mix.
To the same bowl add the butter, egg (just one), and mayonnaise. Mix well.
Shape salmon and crab mixture into approximately 6-8 patties and transfer them to a baking sheet covered with parchment paper. Refrigerate for 1 hour.
After one hour, preheat oven to 400 degrees F. Line a clean baking sheet with parchment paper and set aside. Meanwhile, beat one egg with 1 tablespoon of water and transfer to a shallow bowl. In a separate dish place the fine breadcrumbs.
Remove the pre-formed cakes from the refrigerator and carefully, one-by-one, dip each cake first in the egg mixture, and next in the breadcrumbs to fully coat.
Bake cakes in the oven for 15-20 minutes, or until nicely golden brown.
Serve cakes with rice, fried or poached eggs, mixed greens, fresh fruit, and, of course, tartar sauce, if desired.