Boil and drain the spinach. Squeeze well to drain all the water. Cut into pieces of whatever length you prefer. Drain the tofu, season with salt and pepper, and coat with flour. Mince the onion. Cut the mushrooms into chunks.
Make the onion-miso sauce by combining the ★ ingredients in a bowl, mixing, and setting aside.
Cook the tofu from Step 1 in a frying pan until slightly browned, then remove. In the same frying pan, add onions and spinach from Step 1 and saute. Add mushrooms and continue to saute. Flavor with salt and pepper lightly.
Transfer the contents from Step 3 to a heat-resistant container, then top with the sauce from Step 2. Sprinkle cheese on top and toast in an oven or a oven. Once it's golden brown, it's done.
Story Behind this Recipe
I like the taste of miso and mayonnaise, so I thought about what would happen if I made it into a gratin sauce. Everything used in this recipe was a result of needing to clean out my fridge.
Different misos have different levels of saltiness, so adjust the amount used according to your taste. If the miso is too strong, then the whole thing just tastes like miso. I added yuzu pepper to give a Japanese flavor. If you don't have any, you don't have to use it.