Crush the graham crackers or digestive biscuits in a food processor, or place them in a sealed bag and crush with a rolling pin until fine. Transfer the crumbs to a spacious mixing bowl, then stir in the desiccated coconut and salt until evenly distributed. In a separate large microwave-safe jug or bowl, combine the butter, condensed milk, and cocoa powder. Microwave in 30-second bursts, stirring each time, until the butter is melted and the mixture is smooth and unified. Pour the warm chocolate mixture over the crumb blend and mix thoroughly until the entire mass is cohesive. Refrigerate for 20 minutes to firm up the mixture for easier handling. Using a teaspoon, scoop portions of the mixture and roll them between your palms to shape into compact balls. Roll each ball in powdered sugar until fully coated. Continue forming and coating truffles until all the mixture has been used.