Combine Dry Ingredients: In a large bowl, whisk together glutinous rice flour and baking powder until well-blended.

Heat Wet Ingredients: In a saucepan, combine the milk, sugar, vanilla extract, and salt. Heat until nearly boiling, stirring until sugar dissolves, then remove from heat, add cold butter, and let cool for about 10 minutes.

Whisk Egg Mixture: In a separate bowl, beat the large egg. Gradually whisk in the cooled milk mixture.

Mix Together: Pour the wet mixture into the dry ingredients, then stir gently until a thick paste forms.

Preheat Waffle Maker: Preheat your waffle maker and lightly spray with cooking oil. Scoop about ⅔ cup of batter into the hot iron, cooking until golden brown, around 5-6 minutes.

Release Waffles: Use a chopstick to carefully release the waffles from the iron and let them cool on a wire rack.