Place melon cubes, lemon juice, white sugar
, and a pinch of salt in a blender
and puree for 1 minute. Then add the mint and yogurt
and puree another 1 minute. While pureeing, add the grappa. Transfer the puree to a glass pitcher. Refrigerate. Serve with crostini bread sticks wrapped in prosciutto
to enhance the soup
's sweet flavors.