Melt butter and chocolate using a double boiler method or in the microwave. Let cool slightly while you move to the next step.
In a large bowl beat the eggs and sugars exactly for 4 minutes (set timer, it is important for crackly top). Gradually add to the melted chocolate bowl, add vanilla.
In a separate large bowl, combine dry ingredients. Whisk to combine and add to wet ingredients gradually. Mix until ingredients are almost combined, the batter will be smooth and sticky, like brownie batter.
If it’s difficult to form balls yet, refrigerate for an hour (once balls are shaped, allow to come to room temperature before baking). Overall once the melted chocolate starts to cool and sets, the batter texture should change to ‘’playdough’’ texture and hence be easier to handle.
Scoop 2 tablespoonfuls of dough, rolling it into about 2 inch balls. Dip in powdered sugar (generously).
Arrange the cookie balls on a baking sheet lined with parchment paper at least 3 inches apart. Don’t press down.
Bake for 10-12 minutes or until you get the crackly top. The cookies will have a very soft and moist center inside. Just like fudgy brownies! Let the cookies stand in the pan for 5-10 minutes before transferring to a wire rack.
Notes
Don’t substitute sugars. Both sugars should be used to get the best buttery and soft cookie. You can make these cookies only with white sugar, they will still taste good but there will be a difference.I find that 325 F is better for these cookies rather than the ‘’standard’’ 350 F (but still varies so much on different ovens to be honest). It allows the cookies to take time to spread and get the crackly top without drying them out.