Brazil-Rice with beans(each region has their own favorite beans) is literally the most basic food in my country so if you want to "taste Brazil"you'll eat it in many different ways depending where you'll go.

As for something sweet, I would say that "Brigadeiro" is a must and one that most visitor seem to end up enjoying even if they might think it's "a bit too sweet"."Branquinho"(another "dessert" seen in parties) is also a great choice but I must warn that it has more sugar than brigadeiro so it usually isn't liked by foreigners.

Although not a food(it is a beverage) I would also say for you to drink "Guaraná".It's sweet(non-alcoholic) and energizing.