Line an 8-inch square baking dish with parchment or wax paper.
Combine the white chocolate and sweetened condensed milk in a double boiler over simmering water. Heat until the mixture melts together, whisking occasionally. Stir in the vanilla extract and remove from the heat.
Add all but about 2 tablespoons each of the cranberries and pistachios to the white chocolate mixture, stirring to combine. Spread the mixture into the prepared baking dish in an even layer.
Top with the remaining pistachios and cranberries, pressing them in slightly with a spatula if necessary. Allow fudge to set (this can be done in the fridge) and then cut into 1.5″ squares.