1. Melt the butter over low heat in a saucepan, then add the onions, peas and water.
2. Cook 15 minutes or until tender, remove from heat and cool the mixture slightly.
3. When cooled, stir the milk, mint, salt and pepper into the saucepan and stir well.
4. Pour soup into your blender.
5. Blend until smooth, pour back into saucepan and heat over low heat until warmed through.