Finely chop the onion. Peel the potatoes and cut them into evenly sized cubes.

Heat a knob of butter in a large saucepan over medium heat. Add the chopped onion and potato cubes and cook, stirring, until the onion is translucent and the potatoes begin to soften around the edges (about 5–7 minutes).

Add the spinach and stir-fry briefly until all the leaves have wilted and are well combined with the onion and potato.

Dissolve the chicken stock cubes in hot water and pour it over the vegetables. Season with salt and pepper and bring to a boil. Reduce the heat and let the soup simmer gently for about 10 minutes, until the potatoes are fully cooked.

Remove the pan from the heat and puree the soup with an immersion blender or in a blender until smooth.

Return the pan to very low heat. Stir the yogurt and a pinch of ground nutmeg into the puréed soup and heat only until the soup is warm — do not let it boil again to prevent curdling. Taste and adjust the seasoning with extra salt and pepper if needed.

Ladle the soup into bowls. Enjoy!