Start by crushing the digestive biscuits into fine crumbs using your food processor. If you don't have a food processor, do this by smashing them in a Ziploc bag until they are fine
Mix together the condensed milk and the cocoa powder until the powder is dissolved and well combined. Taste and adjust - if you like a stronger chocolate flavour, add more cocoa.
Remove about ¼ cup of the crushed biscuits and set aside for the topping
Add in the crushed biscuits and mix well until well combined
Refrigerate the mixture for 30 minutes so it can firm up and become easier to roll
Roll about 1 tablespoon of mixture into balls. To avoid it sticking to your hands, dip your hand in a bit of water and spread around your palm, then roll the mixture
Roll the balls in your chosen topping (crushed biscuits, shredded coconut, or any other topping)
Store in an air tight container in the fridge and enjoy!