In a large pan, over medium hot heat, melt the butter and add the onion, fry slowly, covered, for 5 minutes or more, until soft.
Add all the spices, stirring to mix well, cook for a further minute.
Add the flour and stir well, cook for another minute or so.
Add the water and the stock cubes (or the stock and a little salt), stir well, then add the apples and a few generous grinds of the pepper mill. Check the saltiness, and add more to taste. Bring up to the boil, stirring, before reducng the heat and simmering for 15 minutes. Allow to cool a little.
Stir in the chutney and lemon juice and remove from the heat.
In a blender/processor, whizz the soup (careful with hot liquids and blenders!) in as many batches as needed, until smooth and all thoroughly mixed.
In the rinsed-out saucepan, bring the soup back to the boil, then turn off the heat. Season to taste.
You decide if you're serving it hot or cold. If cold, refrigerate and then thin the soup with a little more stock or water, as necessary.
To serve, add a spoonful of yoghurt to each serving bowl of soup.