Preheat oven to 175 C and line a large baking tray with parchment paper.
Simmer the milk, oil, salt together in a small sauce pan and stir the mixture until big bubbles start appearing the milk (approx. 5 minutes.)
Remove from heat and add the flour... give it all a good stir for around 5 minutes. It will start to turn into a semi-gelatinous mixture... which should look like the photo below.
Transfer this dough to a large mixing bowl. After around 10 minutes it should be cool to the touch. Whisk the eggs together in a jug and add them to the mixture in two parts kneading the dough with your hands. You can keep this process all in the mixing bowl as otherwise it gets really messy. At this point add the grated parmesan.
To make the Pao De Queijo you need to roll the batter into little balls around 1.5 inches thick. I sometimes use an Ice-Cream scoop to help me measure the right amount.
Pop the balls onto the baking tray lined with parchment paper, and keep them apart from each other to prevent them from sticking to one another as they rise slightly in the oven.
After 25 minutes remove from oven and let sit for around 5 minutes.