1. Line bottom and sides of an 8-inch square baking pan with aluminum foil.
2. Fill a saucepan with about 1 inch of water and bring to a simmer. Place chocolate in a heatproof bowl and set bowl over saucepan. (Do not allow water to boil or bottom of bowl to touch water.) Cook, stirring often, until about 2/3 of chocolate has melted. Remove bowl from heat and stir until all chocolate is melted and smooth.
3. Use a small metal spatula to spread chocolate in an even layer across lined baking pan. Arrange pretzels on top and sprinkle with cranberries, pressing down gently into chocolate layer. Let bark stand at room temperature until solid, about 45 minutes. Break into pieces before serving.