In a heavy skillet or pot, melt the butter over low heat. Add the condensed milk, cocoa powder, and salt. Whisk until fully combined.
Increase the heat to medium-low. Continue cooking, stirring constantly with a silicone spatula, until the mixture becomes very thick and shiny, and the spatula should leave a clean track when scraped across the bottom. This may take 3 to 4 minutes if you have a hot gas stove or up to 15 minutes on an electric cooktop. It should be balling up into a single mass as you stir. (Do not be tempted to turn up the heat or stop stirring– be patient. Otherwise, the mixture can stick to the bottom of the pot and create lumps or burn.)
Transfer it to the buttered tray. Let cool at room temperature until firm and cool enough to handle, about 1 hour.
With lightly buttered hands, pinch off small pieces of the dough and roll into 1-inch balls. Roll in sprinkles. Place in mini paper cupcake liners. Candies can be stored in an airtight container in the fridge for up to 1 week or frozen for up to 1 month. Delicious served cold or at room temperature.
Notes
Do not walk away from the pot as you make the mixture. If you stop stirring the mixture, it will stick to the bottom of the pot and burn.
The fudge needs to be very firm in order for you to roll them into balls. You’ll need to be patient and continue to stir until the mixture is thick.
Lightly buttering your hands will keep the brigadeiro mixture from sticking to your hands as you roll them. I like to hold onto the butter wrappers as they’re great for greasing your hands without wasting any butter.
Use a cookie scoop to portion out the dough before rolling for uniformed balls.
If you are in a rush, you can chill the tray in the fridge to speed up cooling it to room temperature.