Preheat the oven to 400F. Line a baking sheet with parchment paper. (See Notes, below.)
Add all the first four ingredients to a large bowl and whisk together to incorporate.
In a medium bowl, whisk together the egg, yogurt, cream, and extract. Set aside.
Cut the butter into the dry ingredients until the butter is about pea-sized. The dough will have the texture of crumbs. (See Notes, below. Or see the Scones Primer for pictures.) Reserve a heaping tablespoon of pistachios for glaze. Add the remaining pistachios and the cranberries to the flour mixture.
Add wet ingredients to flour mixture and stir until dry ingredients are incorporated.
Gently knead the dough into a ball in the bowl, then turn out and begin patting into a square until it’s about 1 inch (2.5cm) thick. You may need to squeeze the outer edges a bit to incorporate crumbly bits into the dough.
Cut the dough into roughly 15 or 18 small squares--3 rows of five or six--and place them on the prepared baking sheet. Brush lightly with 35% cream if desired; this gives a nice sheen to the finished scones. (See Notes, below.)
Bake for 11-12 minutes, or until edges start to turn golden.
Let scones cool for about 5 minutes on the pan, then move them to a wire rack. Place the parchment from the baking pan under the wire rack to catch drips when you ice the scones.
While the scones are cooling, make the glaze. Put the chocolate chips in a heat-safe bowl. Pour whipping cream into a glass measuring cup and heat on high in the microwave in for about 20 seconds. Stir and check the temperature; it should be about 175F. Reheat in 5-second increments until it reaches the right temperature. Do not let it come to a hard boil. Pour the hot cream over the chocolate chips and let it sit undisturbed for 30 seconds. Stir until smooth and then let it cool for about 20 minutes.
When scones and glaze have cooled for about 20 minutes, spread the glaze on the scones, then press bits of reserved pistachio into the glaze to garnish.