
This Japanese-inspired salmon gratin combines smoked salmon, tender vegetables, and a creamy soy milk sauce under a golden layer of cheese. A border of mashed potatoes makes it extra comforting and hearty. It is a cozy baked seafood dish that works well for both weeknight dinners and relaxed weekend meals.
Thinly slice the potatoes and arrange them on a microwave-safe plate. Microwave for about 5 minutes, or until very tender, then mash with a fork and season lightly with salt and pepper until smooth enough to shape.

Cut the komatsuna into 3 cm pieces, keeping the stems and leaves separate. Thinly slice the onion, tear the maitake into bite-size pieces, and cut the carrot into short thin strips. Preheat the oven to 250C/480F.

Heat the oil in a frying pan over medium heat. Cook the onion until softened, then add the komatsuna stems and carrot and stir-fry until they begin to soften.

Add the komatsuna leaves and maitake mushrooms, and cook for 1 to 2 minutes until the greens wilt and the mushrooms soften.

Add the butter to the pan and let it melt. Sprinkle in the flour, stir well, and cook for about 1 minute. Gradually pour in the soy milk, stirring constantly, until the sauce becomes smooth and thick.

Fold in the smoked salmon and cook briefly just until combined. Taste the filling and adjust with salt and pepper if needed.

Press the mashed potatoes around the inside edge of a pie dish or shallow baking dish to form a raised border. Spoon the salmon filling into the center and spread it evenly.

Top with the pizza cheese and bake for about 10 minutes, or until the cheese is melted and lightly browned. Serve hot.

Komatsuna can be replaced with spinach or Swiss chard, and shimeji or oyster mushrooms are good substitutes for maitake. Use unsweetened soy milk so the sauce stays savory, and add the smoked salmon at the end to keep it tender. You can assemble the gratin ahead of time, refrigerate it, and bake just before serving.