In a large saucepan, melt the butter and fry the onion with the ginger until the onion is soft, but don't let it brown.
Keeping back 1 tablespoon of the pomegranate seeds, add the rest of the seeds to the pan, along with the spinach and the cumin. Add warm water or warmed vegetable stock (1 1/2 cups / 3/4 pint / 350 ml.) Bring to a boil, then reduce heat and cook covered for about 5 minutes.
Then remove from heat to let it cool slightly. Puree in a food processor or blender (if using blender, cover the top first with a cloth for safety.) Return the soup to the pan. Add the yoghurt, and heat the soup back up but don't let it boil. Adjust taste with salt and pepper.
When you serve into bowls, garnish each bowl with a small swirl of yoghurt and a few of the reserved pomegranate seeds.