How to Make It
Preheat oven to 225°F. Line 2 large baking sheets with parchment paper, and draw 2 (7-inch) circles on 1 parchment paper sheet. Draw 1 (7-inch) circle on second sheet. Turn sheets over, writing side down.
Whisk together potato starch and 1 1⁄2 cups of the sugar in a bowl; set aside. Beat egg whites with a heavy-duty stand mixer fitted with whisk attachment on medium-high speed for 1 minute. Add lemon juice and kosher salt, and beat until blended, about 30 seconds. With mixer running on high, gradually add sugar mixture (2 tablespoons at a time), beating just until glossy, stiff peaks form and sugar is almost dissolved, about 2 minutes. (Do not overbeat.) Reduce speed to low, and beat in vanilla.
Gently spoon egg white mixture evenly onto parchment paper circles. Sift 1⁄2 teaspoon cocoa over each. Using back of a spoon, spread egg white mixture to cover each circle.
Bake in preheated oven until meringues have formed a crust, about 3 hours; rotate baking sheets between top and bottom racks halfway through baking. Turn oven off, and let meringues stand in oven with door closed at least 4 hours or up to overnight.
Chill bowl of stand mixer and whisk attachment 30 minutes. Pour chilled coconut cream into chilled bowl. Add remaining 3 tablespoons sugar. Beat on medium speed, 1 minute. Increase speed to medium-high; beat until fluffy, 3 to 4 minutes.
Place 1 meringue on a serving plate; top with 1 to 1 1⁄2 cups whipped coconut cream. Repeat with 2 remaining meringues and cream, ending with cream. Garnish with chocolate shavings.