For the salmon in filo pastry, wash the salmon fillet and pat dry. Mix the miso paste with the lemon juice and salt and spread on the salmon fillet.
Boil the potatoes in their skins until soft, peel and cut into cubes. Preheat oven to 200 °C top and bottom heat.
Brush one filo pastry sheet with olive oil, place the second pastry sheet on top, twisted 45°, brush edges again with olive oil.
Place the salmon fillet with the marinade in the middle of the pastry sheets, fold the edges over and seal well. Brush dry areas again with remaining olive oil.
Place in oven and bake for about 15 minutes, until filo pastry is brown and crisp. Meanwhile, chop onion and sauté in hot oil until translucent, pour in Soy Cuisine, add sage and salt and simmer for 5 minutes.
Add potato cubes and bring to the boil again. Serve the salmon in filo pastry with the creamy sage potatoes.