In a large mixing bowl, whisk together the glutinous rice powder, cornstarch, and icing sugar. Then add in the rest of the wet ingredients and whisk until no lumps remain.
Brush a little vegetable oil on the bottom of the baking tray (I’m using a 9x9 inch tray).
Sieve the mixture and cover with foil.
Cover and steam over high heat for 8-10 minutes (it should feel firm and lightly springy to the touch, and not stick to your hand). Let cool for a bit (I usually wait until it’s warm enough to handle so that the mochi is still slightly sticky). Then, divide into 4 even squares.Alternatively, you can microwave it for 1 minute in 3 intervals, stirring after each time. Meanwhile, stir fry 1/4 cup of glutinous rice powder in a pan over low heat until it’s heated. Set aside to cool.
Slice and scoop out the mangoes.
Sprinkle some toasted glutinous rice powder onto your work surface (I like doing it on a large piece of plastic wrap to prevent the mochi from sticking).
Place a piece of mochi onto the powder, followed by half of a whole mango. Fold the corners together and pinch to seal shut. Dust with extra toasted powder. Slice in half (or eat as a whole) and enjoy!