Cut the potatoes into 5 mm slices then into bite sized pieces. Saute in butter lightly and season with salt and pepper. Add the milk. Simmer the potatoes until they've absorbed almost all of the milk.
Add water and the soup stock cube to the pan. When it comes to a boil, add the cream stew roux and salmon and mix quickly. Make a sauce that's thicker than the usual cream stew.
Line the bottom of a small casserole or gratin dish with bread. If you toast it beforehand, it will be light and spongy; if you don't toast it, it will be soft and doughy. Choose whichever you prefer.
Put the cooked ingredients from Step 2 in the casserole or gratin dish.
Top with melting cheese and bake in an oven for 5-10 minutes. Done.
If you use salted salmon, it will be too salty. If using salted salmon, use less roux and more milk to adjust the taste.
If you use stew roux, you can omit the soup cube. If you don't use it, saute butter and flour together to make a roux and then make bechamel sauce, or just thicken the sauce with katakuriko dissolved in water.
Story Behind this Recipe
This is a low-effort shortcut recipe. It was surprisingly well received.
If you are short on time, even if the potatoes and salmon are half cooked, just put them in the casserole dish and microwave to cook through. Be careful not to let it dry out or explode! Just top with cheese at the end and brown in an oven, and it instantly turns into a gratin.