In a double boiler, melt the chopped dark chocolate. Alternatively, you can melt the chocolate in the microwave. Let cool while you prepare the next steps.
Combine the dry ingredients: flour, cocoa, baking powder and salt in a bowl. Whisk to combine.
In a stand mixer using the paddle attachment, beat together the oil and the brown sugar and granulated sugar on medium speed for about 2 minutes. It will look crystallized.
Add the eggs, and vanilla. Mix on medium-low until combined.
Next add in the melted dark chocolate and mix on low speed until fully combined.
With the mixer still on low speed slowly add in the flour mixture. Beat until just well combined. The cookie dough will be stiff and slightly sticky.
Place the cookie dough in a clean bowl, cover it with plastic wrap, so that the wrap touches the dough; and refrigerate for 2 hours. This will help prevent the cookies from expanding and spreading out too much while baking.
Preheat your oven to 350 degrees Fahrenheit. While your oven is preheating, let your dough sit out at room temperature for 10-15 minutes.
Line a baking sheet with parchment paper. For each cookies, take a heaping tablespoon of dough and form a ball. Roll the cookie dough ball first in the granulated sugar, then in the icing sugar, till completely and thoroughly covered. Place the balls 3 inches apart on the baking pan. (Rolling the cookie dough first with granulated sugar, was a tip we learned from the baking queen, Sally's Baking Addiction.)
Bake the cookies for approximately 12 minutes. Remove the cookies from the oven and let them rest on the baking sheet for a few minutes before transferring then to a wire rack to cool completely.