Lightly grease a baking tray. In a large bowl, combine the flour, sugar, baking powder and salt. Using a pastry blender or two knives, cut the butter into the flour mixture until the mixture resembles coarse crumbs.
Mix in the eggs, one at a time, until a stiff dough forms. Add the vanilla essence, and stir in the pistachios and cranberries
Divide the dough in half, and shape each half into a 30 x 5cm/ 12 x 2in log on the baking tray. Cover with cling film, and refrigerate the logs for at least 30 minutes.
Preheat the oven to 190°C/375°F/Gas mark 5. Remove the cling film from the logs, and bake for 20–25 minutes until the edges start to brown. Cool the logs on the baking tray for 10 minutes.
Reduce the oven temperature to 170°C/325°F/Gas mark 3. Transfer the logs to a cutting board, and cut crosswise diagonally into 1cm/1 ⁄2in thick slices. Using the same baking tray, arrange the slices so that they lie flat (cut side down) in a single layer.
Bake the slices for 20–25 minutes, turning once, until they are light golden brown on both sides. Cool completely on a wire rack. Store in an airtight container.