Arrange the racks in the top and bottom thirds of the oven and preheat to 250°F. On two sheets of parchment paper, trace six 3-inch circles using a cookie cutter or bowl. Place the parchment on two baking sheets, traced-side-down.

In the bowl of an electric mixer fitted with the whisk attachment, whip the egg whites and salt on medium speed until soft peaks form, about 5 minutes. With the mixer still running, slowly and gradually add the sugar about a tablespoon at a time. When all the sugar is incorporated, increase the speed to high and whip until stiff peaks form, about 5 minutes. (When you lift the head of the mixer, a peak should form on the beater and hold its shape without drooping.) Using a spatula, gently fold in the cornstarch, vinegar and vanilla.

Using two spoons, scoop a mound of the meringue into each circle on the prepared parchment, coaxing it into a round shape. Use one spoon to make a small indentation in the center of each meringue.

Transfer to the oven and bake until the meringues are dry to the touch but not brown, 35 to 40 minutes. Turn off the oven and cool for 1 hour, then transfer to a wire rack to cool completely.

To assemble the birds’ nests, spread about a teaspoon of the melted chocolate into the indentation of a meringue, then top with three Cadbury eggs and some of the toasted coconut. Repeat with the remaining meringues. Stored in an airtight container at room temperature, the birds nests will keep for up to 2 days.