1.Grease 24cm x 32cm (9½-inch x 13-inch) swiss roll pan; line base with two sheets of rice paper, trimming to fit.
2.Stir milk, butter and melts in medium heatproof bowl over medium saucepan of simmering water until smooth. Add marshmallows; stir until smooth. Remove from heat; stir in cranberries and nuts.
3.Spread mixture into pan; smooth surface. Top with remaining rice paper, trimming to fit. Place a second swiss roll pan on top of slice. Weight with cans; refrigerate overnight.
4.Turn slice onto board before cutting.