In a large bowl, whisk the oil, milk, yogurt, vanilla, and sugar for 1 minute until well combined.
Sift in the flour, cocoa powder, baking powder, baking soda, and salt, and mix into a soft, sticky dough.
Cover and chill the dough for 1 hour, until firm enough to scoop.
Preheat your oven to 350°F and line two baking sheets. Scoop 1 1/2 tablespoon balls of dough, roll each first in granulated sugar, then roll heavily in powdered sugar.
The double coating is the secret to bold white crackles that do not melt away in the oven. Bake for 10-12 minutes, until the cookies are puffed and cracked with set edges and soft centers.
Cool on the sheet for 5 minutes, then move to a rack. They firm up perfectly as they cool.
