1.Grease and line base and sides of a 26 x16cm (base measurement) slice pan, extending paper at long sides for handles.
2.Combine milk, butter and chocolate in a medium saucepan over low heat. Cook and stir tor 6-7 minutes or until melted and smooth. Remove from heat. Cool slightly.
3.Process biscuits to make fine crumbs; transfer to a large bowl.
4.Add chocolate mixture to biscuit crumbs; mix well. Stir in cranberries: mix well. Pour into prepared pan. Cover with plastic food wrap; chill for 4 hours or overnight until firm. Cut into slices to serve.
Melt chocolate slowly over low heat or mixture may overheat and curdle; if it does, discard mixture and start again.