Rinse the salt cod thoroughly, place it in plenty of cold water, and refrigerate for 8 to 24 hours. Change the water several times, then taste a small piece; it should be pleasantly seasoned rather than intensely salty.

Drain the soaked cod and simmer it in fresh water for 10 to 15 minutes, or until it flakes easily. Drain well, remove the skin and bones, and finely flake the fish.

Boil the peeled potatoes in lightly salted water for 15 to 20 minutes, until tender. Drain thoroughly and let them steam dry briefly before mashing until smooth.

Melt the butter in a skillet over medium-low heat. Add the chopped onion and cook until soft and translucent, taking care not to brown it.

Combine the flaked cod, mashed potatoes, cooked onion, summer savory, black pepper, and beaten egg. Mix gently but thoroughly until the ingredients are evenly distributed.

Add flour a little at a time, using only enough for the mixture to hold together when pressed. Depending on the moisture in the potatoes and cod, the mixture may need anywhere from 1/4 to 1/2 cup.

Shape the mixture into round patties approximately 1/2 to 3/4 inch (1 to 2 cm) thick. Place them on a lined plate or tray and chill for at least 30 minutes, or up to 1 hour.

Heat a lightly oiled or buttered skillet over medium heat. Fry the fish cakes for 3 to 4 minutes per side, turning once, until browned and heated through; cook in batches if necessary.

Serve the fish cakes hot with mustard pickles, chow-chow, ketchup, or a simple green salad. Avoid very high heat because the outside can brown before the center is hot.