Melt the butter in a pan, add sugar to it, stir it to dissolve. Add the washed currants, peppers, peppermint and cloves. Pour in water, cover and simmer for 15 minutes.
Add finely chopped onions and cook under the lid until the onions are transparent.
Add salt to taste. Then transfer to a blender bowl and beat until smooth.
The sauce can be served warm or cold.