• In a large mixing bowl, combine flours, cocoa powder, brown sugar, baking powder, baking soda, and salt. Using a pastry cutter, cut in cold butter until mixture resembles small crumbs; not all crumbs will be the same size. Stir in miniature chocolate chips. 
• Place yogurt and egg in a measuring cup and whisk well to combine, then add it to the flour mixture. Gently stir with a fork until mostly moistened, and a dough forms.
• Use a rubber spatula (or your hands) to press the dough together, then turn it out onto a lightly floured surface. Knead gently, folding the dough in half over itself, 10-12 times. It's a sticky dough; dip your fingers in flour to keep them from sticking.
• Pat dough out into a 9-inch circle. Cut into 10 wedges and place, separated, on a parchment or Silpat-lined baking sheet. 
• Bake at 375F for 14-18 minutes, until a toothpick inserted in a scone comes out clean. Try again in another spot if you hit a chocolate chip.

Glaze

• Mix together powdered sugar, vanilla, and milk. Spread glaze over warm scones and serve.
• Scones are best on the day they're baked, but leftovers can be stored in an airtight container. Heat for ~8 seconds in the microwave to reheat before eating.

Make Ahead

• Scone dough can be shaped and stored in the refrigerator for 1 day before baking, with no adjustments to the baking time.
• To freeze, cut scone dough into wedges, then frozen. Store in a freezer bag for up to 1 month. Bake from frozen (without thawing), adding 2-3 minutes onto the bake time. Make the glaze after baking.