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 slightly sticky.
Place the cookie dough in a clean bowl, cover it with plastic wrap, and refrigerate for at least 2 hours. This will help prevent the cookies from expanding and spreading out too much while baking. This is a very important step, don't skip it.
At this point, the dough can be refrigerated for up to 5 days or frozen for up to 6 weeks.
Preheat your oven to 350 degrees Fahrenheit. While your oven is preheating, let your dough sit out at room temperature for 5-10 minutes.
Put your icing sugar in a small bowl.
Line a baking sheet with parchment paper. For each cookie, take a heaping tablespoon of dough (we like to use a small ice-cream scoop) and form a ball using the palm of your hands. Roll each ball in the icing sugar, till completely and thoroughly covered. Shake a bit, and roll again in the icing sugar. Place the balls 3 inches apart on the baking pan.
Bake the cookies for approximately 12 minutes. Do not overbake them. You want the inside to be like a brownie. 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. They will be soft, they will harden up as they cool down.
Store at room temperature in an airtight container for up to 5 days.
Enjoy!