Preheat your oven to 350°F (175°C). Gather your tools including an 8x8-inch baking pan, mixing bowls, and a whisk.

In a large mixing bowl, whisk egg whites and granulated sugar until frothy, about 2-3 minutes.

Gradually add the coconut milk to the egg and sugar mixture, whisking continuously. Fold in coconut, glutinous rice flour, and vanilla until smooth.

Pour the batter into the prepared pan, smoothing the top, and bake for about 45 minutes.

Mix reserved egg yolks with a splash of water to create an egg wash and brush over cake after baking.

Broil the cake for 5-10 minutes for a golden top, watching closely to prevent burning.

Let the cake cool at room temperature for about 30 minutes, then refrigerate overnight.

Cut the chilled cake into squares or triangles and serve cold or at room temperature.