Preheat your oven to 350°F (175°C) and prepare an 8x8-inch baking pan by greasing it or lining it with parchment paper.

In a medium bowl, whisk the separated egg whites and granulated sugar until frothy and well combined for about 2-3 minutes.

Gradually pour in the canned coconut milk while whisking continuously, then add the shredded coconut, glutinous rice flour, and vanilla extract. Stir until well incorporated.

Pour the batter into the prepared baking pan and spread it evenly. Bake for 45 minutes until the top is golden.

Brush the top of the cake with beaten egg yolk and broil for 5-10 minutes until golden brown, watching closely to avoid burning.

Let the cake cool on a wire rack, then cover and refrigerate for at least 8 hours, preferably overnight.

Slice the cake into squares or triangles and serve either chilled or at room temperature.