In a medium non-stick saucepan, combine the condensed milk, cocoa powder, and butter. If using, add the heavy cream and salt. Mix well with a wooden spoon or silicone spatula until the cocoa powder is fully incorporated and there are no lumps.
Place the pan over medium-low heat. Stir the mixture continuously, scraping the bottom and sides of the pan.
After about 10-15 minutes of constant stirring, the mixture will begin to pull away from the sides and bottom of the pan.
Immediately pour the hot mixture onto a greased plate or shallow dish.
Allow the mixture to cool to room temperature (1-2 hours).
Lightly butter or oil your hands. Scoop out portions about the size of a walnut.
Gently roll each portion between your palms to form smooth balls.
Roll each ball in chocolate sprinkles, ensuring complete coverage.
Transfer each coated brigadeiro to a small paper candy cup.
