Microwaving the chocolate helps keep the temperature below 92°, ideal for tempering. Use the best-quality white chocolate you can find (not those labeled "baking chips").
Place chocolate in a microwave-safe bowl. Microwave at 20% power for 15 seconds; remove bowl from microwave and stir. Repeat process until most of the chocolate has melted and is smooth. Let stand, stirring occasionally, until all of the chocolate melts and is smooth.
Set aside 1 tablespoon each cranberries and pistachios.
Stir remaining cranberries and remaining pistachios into chocolate. Spread mixture onto parchment paper in an even (1/4-inch-thick) layer. Top evenly with reserved cranberries and pistachios, and sprinkle evenly with salt, pressing gently to adhere. Refrigerate 1 hour or until set. Break into bite-size pieces.