Pour the sweetened condensed milk into a pot, turn on medium heat, and stir continuously to prevent the milk from sticking to the bottom. Once you see small bubbles forming on the surface, turn off the heat immediately.

Gradually sift the cocoa powder into the pot and mix well. Don't add all the powder at once, as it will be hard to mix. Adjust the amount of cocoa to your taste; use about 3 1/2 ounces (100 grams) for a sweeter taste, or 7 ounces (200 grams) for less sweetness. If you use too little cocoa, the mixture will be too runny to shape.

Mix until the mixture becomes thick and chewy. Taste to ensure it's sweet enough for your liking. Take a container, line it with plastic wrap, and spread a little butter or oil to prevent sticking, although the plastic wrap should suffice. Spread the mixture evenly (this part is very sticky!) and cover with another layer of plastic wrap, pressing down to smooth the surface.

Refrigerate for 2-3 hours or freeze for 1-2 hours. It should be firm before proceeding. Sift a thick layer of cocoa powder onto a cutting board/plate to prevent sticking. Remove the plastic wrap, place the chocolate on the board, and cut into small pieces about the size of a fingertip, shaping as desired. Coat the pieces with cocoa powder to prevent them from sticking together. Store in a container in the fridge. Note: This treat is a bit sticky on the teeth.