Preheat the oven to 350 degrees.
In a large bowl combine the flour, baking powder, baking soda, salt, and lemon zest.
Either cut cold butter into small pieces or grate frozen butter and add to the flour mixture. Use your hands and combine the butter with the flour mixture until pea sized dough balls form.
In a medium bowl combine the sugar, egg, sour cream, and lemon juice. Mix well.
Add the sour cream mixture to the dry ingredients and mix until a dough forms.
Turn the dough onto a floured cutting board and shape into a circle that is about 3/4 inch thick.
Using a pizza cutter, cut the circle into 8 pieces.
Place the scones on a greased cookie sheet 2-3 inches apart.
If desired sprinkle with the coarse sugar.
Bake for 20-22 mintues or until the bottoms have browned.
Remove from oven and cool completely.