To make the starter-dough: Mix ¼ cup of sticky rice flour and 2 tbsp of whole milk together in a microwave-proof bowl. Microwave on high for 50 ~ 60 seconds until the dough is cooked through, which will look opaque and feel very 'bouncy'. Set aside to cool for 5 min.

To form and fry the donuts: Meanwhile, add 1 ¾ cup of sticky rice flour, ½ cup of milk, melted butter, granulated sugar, egg and baking powder in a stand-mixer bowl with dough-hook. Add the cooled starter-dough and knead the mixture on low until everything comes roughly together, then increase the speed to medium and knead until the starter dough has completely blended into the mixture.

Scrape the dough onto a surface that’s dusted with more sticky rice flour. Sprinkle just enough sticky rice flour onto the dough to prevent sticking, then roll it into ½" (1.3 cm) thick. Cut out donuts using a well-floured cutter.

Add enough canola oil to a frying-pot to reach 1 ½" deep and set on medium-high heat to bring the oil to 330ºF/165ºC, then turn the heat down to medium-low. Carefully drop a few donuts into the oil and fry for a few minutes on each side until puffed up and golden browned. Transfer to a cooling rack to drain.

Mix 2 ½ tbsp of melted unsalted butter with powdered sugar and vanilla extract, then add 2 ~ 3 tbsp of hot water to bring it to a desired glaze-consistency. Dip one side of the donuts into the glaze and serve within a few hours.