If you purchased pre-grated cheese, skip to next step. Grate the parmesan and shred the mozzarella. After measuring out the required amount, you can mix the cheeses together in a bowl and set aside.
Preheat oven to 400°F.
Set up your stand mixer so that it's ready to go for the next step. Add the tapioca flour and baking powder to the bowl of the mixer.
In a medium-sized saucepan, combine the wet ingredients (milk, water, oil and salt). Cover and bring to a gentle rolling boil over medium heat. Once boiling, pour over the flour in the mixer.
Turn on the mixer and mix on high until the tapioca flour and wet ingredients are well-incorporated. It will have a stretchy, sticky texture that is to be expected.
Add eggs one at a time. To make things easy, you can crack the two eggs into a small bowl and whisky gently. Pour this in a slow steady stream into the mixer on medium-high speed. Allow the eggs to incorporate in small increments before adding more.
Repeat a similar process with the cheese. Working in small batches, add the cheese into the batter slowly until fully combined.
Spray your mini muffin tin with non-stick spray. Using a small scoop or spoon, scoop the batter into the muffin wells.
Bake for 15-20 minutes, until puffy and golden.