Pour the milk, chocolate powder and 1 tablespoon of the butter into a medium sauce pan. Stir with a silicon spatula until smooth.
Place over medium or medium-high heat and stir constantly until beginning to bubble around the edges. Reduce the heat to maintain a slow simmer.
Continue stirring until the mixture darkens and thickens. Adjust the temperature if necessary to keep the mixture from burning. You want to slowly caramelize it without burning or sticking. Be careful to scrape the sides and bottom of the pan well.
After about 10 minutes (give or take a few minutes) the mixture should be quite thick and, when you tilt the pot up it should sort of fall away from the bottom of the pot. This is called ponto de brigadeiro (See the video for a demonstration of what to look for).
Turn off the heat.
Smear a little of the reserved butter onto either a plate or a marble slab and spread the mixture out into about an 8″ disk. Let cool about 5 minutes or until cool to the touch.
Lightly oil your hands with butter and roll the mixture into small balls about the size of a large grape. Coat in sprinkles and place each brigadeiro into a paper candy cup.
These will keep in a container at room temperature for about 3 days.