Preheat the oven to 375°F. Line a baking sheet with parchment paper.
In a large bowl, whisk together the dry ingredients (through salt). Cut in the butter with a pastry blender until the mixture is crumbly (or use clean fingers to work it together). Add the cranberries and orange zest and stir with a fork. Add the egg and buttermilk and stir with a fork until the dry ingredients are just moistened.
Gather the dough into a ball and place on the baking sheet. Pat into a 7-inch circle. Cut into 8 wedges with a knife dipped in flour. Do not separate the wedges.
Bake until golden brown, about 20 minutes. Transfer to a baking rack to let cool. Sprinkle with powdered sugar while still warm. Cut through the wedges with a serrated knife and serve.
Notes
If you'd like to sweeten things up, you can add a glaze to the tops of the scones. In a medium bowl, whisk together one cup of powdered sugar with ½ teaspoon vanilla extract and 1½ tablespoons of milk. Drizzle the vanilla glaze on top of the scones and let them sit until the glaze has firmed up a bit.