A day before you plan to serve the dessert, heat the oven to 300 degrees for at least 15 minutes, then turn it off and leave the door closed. Whip the egg whites until foamy in a mixer fitted with a whisk attachment. Add the granulated sugar and whip until stiff and glossy, about 3 minutes. Add the confectioners' sugar and whip very briefly (I count to 10), just to incorporate.
Spoon the mixture into a pastry bag with a medium plain tip and pipe small hearts with 2 teardrop shaped strokes onto a parchment lined cookie sheet. Place the pan in the turned-off oven, close the door, and leave overnight to dry until crisp. (The recipe can be made up to this point and stored at room temperature in an airtight container up to 5 days in advance.)
When ready to serve, whip the cream and place in a pastry bag with a star tip. Place 1 meringue heart on a plate then pipe on cream. Top with raspberries and a final meringue. Tuck a mint leaf into each, sprinkle with powdered sugar and serve.
I use only egg whites and air which makes for an extremely light texture but completely crisp and dry rather than creamy or smooth.