Preheat the oven to 325ºF (160ºC) and have a standard half-sheet 17-¼ x 12-14 inches (44 x 31-cm) baking sheet ready. Cut a piece of parchment paper to fit the baking sheet.
In a large bowl, whisk together the flour, powdered sugar, and salt.
Add the melted butter and orange blossom water to the flour mixture and stir until all of the dry ingredients are combined.
Fold in the chopped dried cranberries, pistachios, and white chocolate. Stir until well combined.
Place the sheet of parchment paper on a work surface and dump the shortbread dough on top.
Gather the dough into a rough disc with your hands. Using your fingertips, gently press the dough all over, working it into a smooth round disc.
Still using your fingertips, continue to work the dough gently, shaping it into a rectangle shape, about 7 x 8-inches (18 x 20-cm) in size and ¼-inch (6-mm) thick.
A bench scraper or the edge of a long knife can help create straight edges as you go.
Once the shortbread dough is pressed into shape, gently slide your hand under the parchment paper and transfer the shortbread dough to the baking sheet.
Place the baking sheet in the pre-heated oven and bake the shortbread slab for 33 to 35 minutes, or until the dough is lightly golden around the edges.
Remove the shortbread from the oven and carefully transfer the hot cookie slab, still on the parchment paper, to a cutting board (we used two large spatulas to do this).
Using a long, sharp knife, slice the cookie slab into individual squares or rectangles while still hot.
Transfer the sliced shortbread cookies to a wire rack and let them cool completely before serving or packaging as gifts.