Line two baking sheets with parchment paper and set aside.
In a medium saucepan, combine butter, milk, sugar, and cocoa powder.
Bring to a rolling boil over medium heat, stirring constantly. Let boil for 1 minute, then remove from heat.
Stir in peanut butter, vanilla extract, and salt until smooth.
Add oats, cranberries, and walnuts. Stir until fully combined.
Drop spoonfuls of the mixture onto prepared baking sheets.
Let cookies set at room temperature for about 30 minutes, or refrigerate to speed things up.