Melt the butter over low heat. Dissolve the yeast in the water and add the butter. Add the salt and wholemeal flour. Stir well, then add enough plain flour until the dough is no longer sticky. Knead for approx. 5 minutes then let rise on the tabletop until around double in size.
Rinse the spinach and put in a pan with butter. Sauté until wilted. Pour off any excess liquid. Add the cheese in cubes and stir until it is worked into the spinach. It’s okay if there are little lumps of cheese left. Finally, cut the salmon into little pieces and add to the spinach mixture. Season to taste with salt, pepper and grated nutmeg. Let the mixture cool slightly.
Roll out the dough thinly and cut into circles with a diameter of approx. 15 cm. Place a spoonful of filling in the circle and fold the dough over. Fold up the edges so they don’t open during baking.
Bake the pierogis at 180°C for about 12 minutes. Can be enjoyed hot, warm or cold.