Pão de queijo ("cheese bread" in Portuguese) is a small, baked cheese roll or cheese bun, a popular snack and breakfast food in Brazil. They are similar to French gougère but are naturally gluten free. There are several different recipes where the ingredients may vary widely, as well as the final result. Some of them use sweet starch, other sour, or even both. But what gives it its main feature is that it is based on cassava starch and some kind of cheese. You can read more about it here.
Its culinary roots can almost certainly be traced back to the landlocked state of Minas Gerais in south-east Brazil. It's thought that the indigenous Guaraní peoples pounded native cassava, otherwise known as yuca or manioc, to make basic bread long before the arrival of the Portuguese in 1500. When the colonisers settled in Minas, bringing with them African slaves, the colonial capital Ouro Preto was at the heart of the Brazilian gold rush, they discovered that the land wasn't suitable for cultivating grains like wheat, and turned to this hardy, starchy tuber. Like bitter almonds, cassava root contains cyanide and rendering it edible was a laborious process; it had to be peeled, finely grated, soaked in water and dried. This left behind a residue of powdery tapioca starch that the slaves, desperate to boost their paltry diet, would scrape out of the bowls and roll into small balls of dough before baking. Fast-forward to the late 19th century; slavery was abolished, cattle farms were widespread, and salty, aged Minas cheese, milk and eggs were added to the mix, and this historic snack went nationwide.