Before starting, put your butter in the freezer for at least 15 minutes. Preheat the oven to 425F/218C degrees. Then, grate the frozen butter with a cheese grater. Place it back in the freezer.
In a bowl, whisk the milk and sour cream together and then put into the fridge. Grate the skin off a lemon or orange into a large bowl. Add in the the flour, baking soda, baking powder, salt and ½ cup sugar and stir together. Lightly dust the countertop with flour.
Get the grated frozen butter and toss it with the flour mixture until all the butter is coated. Fold in the chilled milk and sour cream mixture and combine until the batter is quite wet. Turn out onto the floured countertop and with floured hands, knead it about six times. Do not over knead it.
Roll the dough with a rolling pin into a 12-inch square. Fold it in half, and then fold again, like folding a napkin. Put it on a plate or similar and put into the freezer for about five minutes. This will rest the dough plus slightly refreeze the butter, yielding a more flaky pastry.
While its in the freezer, dust your countertop with flour again and put a heavy cookie sheet or baking stone into your preheated oven to get it warm. (You might want to use these few minutes to make yourself a cup of tea.)
After five minutes, remove the doll and roll your square flat into a 12-inch square. Push the dried cranberries into flattened batter, then spoon the marmalade into a light layer over top. Roll up the dough and turn it over if necessary so the seam is on the bottom. Gently push the roll down until it’s about three inches wide.
With a sharp knife, cut the roll into a series of triangles. Brush the top with the beaten up and sprinkle lightly with the remaining sugar. Place the triangles on the preheated cookie sheet and bake for 15 minutes or until medium brown. Let the scones rest at least 15 minutes before serving.