This recipe comes from a 2004 issue of Gourmet magazine, though I have adapted it a bit. I've made it dozens (if not hundreds!) of times over the years, and it always gets rave reviews -- my friends ask me to make it for every gathering I host or attend.
One note: If no peaches or nectarines are available or the ones available look a bit dodgy, you can use mango instead. —Marshmallows&Margaritas
Rinse the mint leaves, dab them with a paper towel, and place them in a small food process with the sugar. Pulse to combine. (If you don't have a small food processor, chop up the mint leaves into small pieces and stir together with the sugar)
Wash off all the fruit. Add the blackberries to a serving bowl, then cut the peaches into roughly 1 1/2-inch pieces and add those to the bowl. Cut the grapes in half and add them, then stem and quarter the strawberries and add them.
Add mint sugar to fruit and stir to combine. Cover the bowl and chill the fruit for at least 10 minutes or up to an hour, then stir and serve. If making farther ahead of time, combine all the fruit and wait to add the mint sugar until shortly before serving -- otherwise the sugar will break down the strawberries and make them mushy.