Preheat oven to 325 degrees. Line the bottoms and sides of an 8x8 baking pan with parchment and set aside.
Combine the butter, sugar, cocoa and salt in a medium heatproof bowl. Set the bowl on top of a small pot of near boiling water to create a double boiler. Stir the ingredients until the butter melts (the ingredients will look a bit grainy). Remove the bowl from the heat and allow to slightly cool, about 2-3 minutes. Stir in the vanilla. Add the eggs, one at a time, stirring with a wooden spoon between each addition. Add the flour and beat vigorously, until all the flour is incorporated and the mixture becomes smooth. Gently fold the cranberries into the batter, being sure to reserve some to sprinkle on top. Evenly spread the batter into the prepared pan and bake for 25-30 minutes, but no more than 35 minutes, until a tester inserted into the center comes out nearly clean (you don't want it to come out completely clean, or it means your brownies are overcooked). It is likely that the brownies will not look "done." Remove the pan from the oven anyway and allow it to cool to nearly room temperature. Remove the brownies, keeping them on the parchment, and set on a cooling rack. The brownies will firm up as they continue to cool.