Wash the poulard and dab dry. Wash the lemon with hot water, grate the peel and squeeze the juice. Rub the poulard with lemon juice, salt and lemon pepper. Place on a baking tray and bake in a preheated oven (electric range: 200 °C/ gas: level 3) for about 1 hour.
Wash, clean and sort the spinach thoroughly. Clean, wash and slice the mushrooms. Peel and finely chop the onion. Heat the fat in a pot and fry the diced onion and mushrooms.
Add the spinach and stew for about 5 minutes. Season with salt, pepper and nutmeg. Remove the poulard and arrange it on a plate with the spinach. Sprinkle with lemon peel and garnish with lemon balm and lemon slices.