Grease a heat proof plate or baking sheet.
In a thick-bottomed pot add condensed milk, cocoa powder, salt, and butter. Mix well. (Also add the additional flavoring ingredient if using.)
Cook on medium-low heat the mixture for 15 minutes with constant stirring. Cook until the mixture gets thick and leaves the sides of the pan forming a ball like soft dough. Adjust heat if the mixture is sticking to the bottom. Keep scraping the sides with a spatula.
Pour mixture on a greased plate and let it cool for 25 minutes.
When the mixture is cool enough to handle roll out a small ball and tuck an almond in it hiding it completely. Repeat to make more balls.
When all balls are ready, roll each ball in the desired topping or simply in the chocolate sprinkles. Brigadeiro truffles are ready to serve. Store at room temperature or in the fridge for 3-4 days. These start drying after 12 hours and lose it chewy softness.