Place the chocolate and butter in a microwave-safe bowl or in the top of a double boiler. Microwave at 80 percent powder or heat over (not touching) barely simmering water, stirringing occasionally, until melted and smooth. Let cool.
In a large bowl, combine the cooled chocolate mixture and granulated sugar. Add eggs, one a time. Add vanilla. Whisk together flour, baking and salt. Mix in.
Cover the dough with plastic wrap and chill for 3-4 hours or overnight.
Preheat the oven to 350° F. Lightly grease a cookie sheet.
Scoop 1-inch pieces of dough and roll into balls. Roll in powdered sugar to coat evenly. Place on prepared baking sheets about 2 inches apart. Bake 12-15 minutes, until tops are set and surface looks crackled. Let cool on cookie sheets for 2 minutes, then transfer to wire racks to cool completely. Store in airtight container at room temperature for 5-7 days.
Notes
The dough is very sticky, so chilling the dough is an absolute must. Chill for 3-4 hours or overnight. I usually chill overnight.
I recommend using a cookie scoop to help ensure cookies are the same size and bake evenly.
To help work with the sticky dough, chill the cookie scoop beforehand and prep one tray of cookies at a time, working quickly. Roll several cookie dough balls at once. Keep the dough and the cookie scoop in the fridge between batches.
Generously coat the dough balls in powdered sugar. Resist the urge to press the balls down on the cookie sheet; they'll work their own magic in the oven, I promise.
Store chocolate crackle cookies in an airtight container for up to a week. Freeze baked cookies in an airtight container for up to 2 months. Place waxed paper or parchment paper between layers. The powdered sugar may smudge a bit when stored and thawed.
Make-Ahead Tips: You can make and chill the dough 1-2 days in advance. Roll in powdered sugar just before baking. Unbaked cookie dough balls can also be frozen for up to 2 months. Thaw in the refrigerator overnight, then roll in powdered sugar before baking.