Preheat oven to 425°F. Spray a baking sheet with cooking spray.
In a bowl, combine flour, cream of tartar, baking soda, salt, and orange zest. Use a pastry blender or two knives to cut in butter until mixture is crumbly. Mix in Splenda Stevia Sweetener.
Pour milk over dry ingredients and stir just until dry ingredients are moistened. Stir in cranberries and pistachios.
Transfer dough to lightly floured work surface and knead gently to incorporate any loose flour. Pat into a ¾-inch thickness. Cut scones with a 2½” round cutter, and place on cookie sheet. Reuse scraps if needed.
Bake for 12–15 minutes or until pale golden brown.