Use a mandoline to get perfectly thin and even slices. This was from 4 potatoes.
Prep the onion and shred the cheese. Set aside ½ to 1 cup of cheese for the final step in baking. It was a big onion so I diced the whole thing and will store in the fridge for use in another recipe in a few days.
Preheat your oven to 180° C (350° F), grease a 9x13 baking dish with butter or cooking spray.
Whisk together the soup and milk in mixing bowl and set aside.
Layer the bottom of the baking dish with half of the potatoes.
Sprinkle with 1½ tablespoons flour and add salt and black pepper as desired.
Sprinkle on half the onion, half the salmon, and half the cheese.
Add the remaining potatoes in a layer. Then the remaining flour, salt and pepper, then the remaining onion, salmon, and ending with cheese.
Pour the soup mixture over the top
Cover with foil and bake for 45 minutes or until potatoes are tender, this may take longer than 45 minutes depending on the thickness of the potato slices. Remove foil.
Sprinkle with the reserved cheese.
Bake uncovered now for another 10 to 15 minutes until cheese is bubbly and starting to brown.
Serve as a side or a main dish, and enjoy .