Preheat oven to 200˚F. Line baking sheet with parchment paper.
Make cakes: Microwave kaffir lime leaves 10 seconds. Toss leaves and repeat process until they are dry and brittle, 10 to 12 times. Use coffee grinder to grind dried leaves into fine powder. Remove any stems that remain. Set lime leaf powder aside.
In bowl of stand mixer fitted with whisk attachment, whip egg whites, cream of tartar, and salt until frothy. Gradually add granulated sugar, continuing to whip until firm peaks form. In small bowl, sift together ¾ teaspoon of lime leaf powder and confectioners’ sugar. Fold confectioners’ sugar mixture gently into egg white mixture.
Spoon mixture onto prepared baking tray to form 6 mounds. Use back of spoon to spread each mound into round meringue about 4 inches wide with slight indentation in middle. Sprinkle another ¼ teaspoon of lime leaf powder over meringues. Bake meringues 1 hour and 15 minutes. Allow to cool completely in pan.
Make macerated mangoes: Peel and pit mangoes and cut flesh into ½-inch pieces. In medium bowl, stir together mangoes, sugar, salt, lemon juice, lemon zest, ½ teaspoon lime leaf powder, and coconut. Allow to macerate 2 hours.
Make cream: whipping heavy cream in stand mixer fitted with whisk attachment until medium peaks form.
To serve, place baked meringue cakes on cake stand or in individual serving dishes. Top with dollop whipped cream, macerated mangoes, and light dusting of confectioners’ sugar.