Heat oven to 425 degrees.
Mix together in a large bowl the gluten-free pastry flour, sugar, baking powder, baking soda, salt, and xanthan gum.
Cut the cold unsalted butter into pieces and drop it into the flour mixture.
Cut the butter in with a pastry blender or two knives until the largest pieces of butter are pea-sized.
Stir in chopped nuts and/or dried fruit if using.
Whisk together cream and egg in a separate bowl, adding orange or lemon zest if desired.
Add wet ingredients to dry ingredients and stir until the mixture starts to hold together.
Gently knead the dough a few times with your hands, adding more cream if the dough is too dry.
Put the dough on a baking sheet and shape it into a flat disk about one inch high.
Cut into eight equal pieces and arrange them on the baking sheet about one inch apart.
Brush some cream onto the tops of the scones.
Bake for 10-12 minutes, or until a toothpick inserted into the middle comes out clean.
