Servings10 to 12 slices per log
To a saucepan over medium heat, add the condensed milk, butter, cocoa powder, and heavy cream. Cook, stirring constantly, until the butter is melted and the mixture is smooth and glossy.
Lower the heat and stir in the chopped chocolate, vanilla extract, and salt until fully melted and combined. Remove from the heat.
In a large bowl, add in the chopped tea biscuits and walnuts, pour the chocolate mix over, and use a rubber spatula to fold gently until everything is evenly coated.
Divide the mixture evenly between two pieces of plastic wrap. Shape each portion into a log, then roll tightly to seal.
Refrigerate until firm, at least 2 hours. Unwrap, dust the logs generously with powdered sugar, then slice and serve.