Put the water in a small saucepan with milk, butter, and a pinch of salt. Let the butter melt without the water coming to a boil.
Add all the powders (rice flour, starch, and starch sifted together) in one go. Mix well and cook until a ball forms and comes away from the sides of the saucepan.
Then pour the resulting mixture into the mixer and let it cool while slowly turning.
Beat the eggs and add them a little at a time in the mixer, letting the mixture combine well before adding more. You can do this step by hand, stirring the mixture with a whisk.
Lightly butter a baking sheet. Using a pastry bag, shape into small walnuts and lightly crush the tips with a wet finger to make sure they grow evenly when baking.
Bake in a hot oven at 220°C (428°F) for the first 10 minutes. Lower the temperature to 190°C (374°F) and bake for another 15 minutes. Turn off the oven, and slightly open the oven door so that the steam can evacuate and the puffs dry before taking them out of the oven.