Soak cranberries in a small bowl covered with warm water. Soak until plumped (about 15 minutes). Drain, pat dry and set aside.
In a large bowl whisk together flour, baking powder, and salt.
In another large bowl, using an electric mixer, beat together butter, 1 cup sugar and vanilla until fluffy (about 2 minutes). Beat in 3 of the eggs until well blended (about 2 minutes longer). Gradually stir in the flour mixture and beat until smooth (about 3 minutes). Stir in the cranberries and whole pistachios.
On a lightly floured surface, divide the dough in 1/2. Shape each half into a log 11 inches long by 1-1/2 inches in diameter.
In a small bowl, beat together the remaining egg and water. Brush the top of each log with the egg mixture and sprinkle with the tablespoon of sugar.
Place the logs, well spaced, on an ungreased baking sheet and press down to flatten slightly. Bake for 25 minutes or until slightly colored and firm to the touch. Transfer the baking sheet to a wire rack. Leave the oven on.
When the logs are cooled (about 10 minutes), transfer them to a cutting board and cut on the diagonal into slices about 3/4 inch thick. Bake for 6 minutes or until lightly golden. Turn the slices over and bake until the second sides are golden, about 5-6 minutes longer. Transfer to a wire rack to cool.
Melt chocolate in the top of a double boiler set over gently simmering water. Remove from the heat. Working quickly, dip 1/3 of each cookie into the chocolate, and then dip the chocolate covered tip into the chopped pistachios. Return cookies to the rack until the chocolate is set.
Set the chocolate back over the double boiler to re-melt the chocolate if necessary. Store in layers, separated by waxed paper, in an airtight container at room temperature for up to 1 week.