Preheat your oven to 350 and place unseasoned fish on baking tray. Bake for 12 minutes, until opaque. Remove from pan and chill for 10 minute in refrigerator.
In a large bowl, mash the baked potato and flake the chilled cooked fish into it. Add the rest of the ingredients and combine until a mixture forms. To form patties, use a 1/3 cup measure to scoop and form or use hands to shape into discs. Coat with panko and refrigerate for an hour before frying.
In the meantime, preheat oven again to 350F and in a large saucepan, heat 1/2 inch vegetable oil. Fry the cakes on each side until golden brown (3 minutes each) and then bake until heated through. To make sauce: whisk all ingredients together.