Preheat oven to 350 degrees. In a bowl, add sour cream and baking soda. Mix to blend.
Whisk together flour, sugar, baking powder and salt in a large mixing bowl. Mix butter in using a pastry blender or two knives in a criss-cross fashion, until butter is broken into small morsels in the flour.
Beat egg and mix into sour cream. Add sour cream mixture into dry mixture, working it in.
Dough should be a bit dry, and use your hands to combine it. If needed add milk until combined. Aim for having drier dough, and careful not to overmix.
When dough is combined, fold in the cranberries by hand.
Divide into three equal circles, patting each into a circle that is one inch thick (width ranges from 6-7 inches). Cut each circle into six triangles.
Bake on a well butter greased lined baking sheet for 15-20 minutes, until scones are browned nicely on the bottom and slightly on top.
Top with a sprinkle of sugar (optional) and serve warm or chilled.