Preheat the oven to 350°F (180°C) and line a baking sheet with parchment paper.
In a medium size bowl, whisk together the pumpkin puree, brown sugar and egg until it is all well incorporated. Now whisk in the vanilla and sour cream and set aside.
In a different bowl mix together the flour, cinnamon, ginger, nutmeg, salt, baking powder and baking soda.
Using a processor, process the previous flour mixture along with the white vinegar and butter cubes until you get a sand-like concistency. (You can also achieve this by grating the butter while cold and mixing it with the rest of ingredients using forks).
Knead only a little to bring it all together into a ball and place it on the kitchen counter. Form a circle about 1/2inch (1cm) thick and cut 6 triangles, like you would a pizza.
Place the pieces on the baking sheet and brush to coat them with the egg and milk mixture, and bake to 350°F (180°C) for about 15 minutes.
For the glaze:
In a small bowl, mix together all the ingredients, and once the scones cool down a little, glaze them.