Preheat the oven to 200C/180C Fan/Gas 6. Line a baking tray with baking parchment.
In a large bowl, mix together the flour, salt, baking powder, caster sugar and caraway seeds. Using your fingers, rub in the butter until the mixture resembles breadcrumbs. Mix in the cranberries and orange zest.
Mix the egg and buttermilk together then stir into the dry mixture using a wooden spoon. Use your hands to bring the dough together, then turn out onto a lightly floured surface and shape into a ball.
Place the dough on the prepared baking tray and cut a cross into the top using a sharp knife. Bake for 30–35 minutes, or until risen and golden-brown. Cool completely on a wire rack before serving.