Preheat the oven to 325℉ and line your cupcake pan with liner. You can also use cupcake cups in a baking sheet. Alternatively you can brush on melted butter into the cupcake pan.
Separate the egg into yolk and whites. Save the egg whites for later.
Combine milk and oil together, whisk until they are emulsified.
Add in egg yolks and whisk.
Sift in glutinous rice flour and whisk.
Set aside the mixture. In a different bowl, add a few drops of lemon juice or white vinegar to the egg white. Add in sugar and whip until when you lift up whisk it When you lift up the whisk there should be a slight curve to the tip.
Whisk 1/2 of egg white into your egg yolk mixture. Then add the egg yolk mixture into the egg whites. Fold until it's fully incorporated (no egg whites shown through).
Pour the mixture into the cupcake pan or cupcake cups. It should be about 90% full. Put some melted butter in between the cupcakes to prevent sticking. It will rise as it bakes.
Optional: sprinkle some white sesame seeds on top.
Bake in the oven for 35 minutes.
