Lingkan Reang
Preheat oven to 150°C and line an 18 cm square cake pan with parchment paper.
Sieve flour, then mix warm butter and milk into it, followed by egg yolk and vanilla.
Beat egg whites until frothy, then gradually add sugar and whip until fluffy.
Gently fold the egg yolk mixture into the whipped egg whites.
Pour batter into the prepared pan, place it in a larger pan with hot water, and bake for 30-35 minutes.
Cool for 2 minutes, remove from the pan, unwrap the parchment, slice, and serve.