Heat the olive oil and fry the chopped onion over moderate heat, for about 3 minutes, stirring occasionally so that the onion cooks evenly.
Then add the chopped cucumber, grated lemon rind and stock. Bring the liquid to a gentle simmer and simmer for 4-5 minutes.
Take the pan off the heat, cool the contents, then whiz with a hand-held blender until smooth, adding the mint leaves at this stage. As they are whizzed they will fleck the liquid with green.
Taste, and season with salt and pepper.
Stir the yoghurt through the soup and store in a covered container in the fridge for half an hour before serving.
If you like, float a mint leaf on each serving of soup and serve with Nairn's Oatcakes.
1 tbsp olive oil
1 onion, skinned and chopped
1 cucumber, skin peeled off with a potato peeler, the cucumber halved lenghways and the seeds scooped out using a teaspoon. Chop the cucumber
Finely grated rind of a ½ lemon
½ pint/300mls stock - this can be a good stock substitute, e.g. Marigold powder made up with boiling water
Salt, to taste, and about 15 grinds of the peppermill
A small handful of mint leaves, stripped from the stalks
½ pint/300ml yoghurt
Serve with 3 Nairn's oatcakes, variant of your choice