Add mulberries in a blender and blend to make a smooth puree.
Add the puree in a bowl and add sugar and lemon juice and mix well.
Transfer the puree in 2 serving glasses.
Top the glasses with club soda.
Garnish with mint leaves and serve immediately.
Mulberries spoils very quickly. Try to use them immediately. They leave stain on your hands and clothes, so be careful. This drink should be made just before serving. You can increase or decrease the sugar according to your taste.