Place chocolate in a small microwave-safe bowl. Heat for 60 seconds on 50% power, stir, and continue heating for 10 seconds at a time on 50% power, stirring after each heating until completely melted. Set melted chocolate aside to cool.
MIX COOKIE DOUGH:
In a large bowl, beat together oil, sugar, and melted chocolate on medium speed until combined.
Add eggs one at a time, mixing well after each addition. Add vanilla and beat until incorporated.
In a small bowl, whisk together flour, baking powder, and salt. Gradually add flour mixture to wet mixture until well combined, and no flour streaks remain. (The dough will be very wet; chilling it will harden the dough.)
CHILL COOKIE DOUGH:
Cover the bowl with plastic wrap and chill cookie dough in the refrigerator for at least 2 hours or overnight.
Remove cookie dough from refrigerator and set on the counter for about 20 minutes to warm up slightly.
PREP OVEN AND BAKING SHEETS:
Move oven racks to the upper-middle and lower-middle positions. Preheat oven to 350 degrees. Line baking sheets with parchment paper or silicone mats.
Place powdered sugar in a medium bowl. Roll cookie dough into balls and then roll the dough in powdered sugar until coated.
Bake for 10-12 minutes or until the edges of the cookies are set. Remove the cookie sheets from the oven and let the cookies set on the baking sheets for 2-3 minutes.
COOL AND SERVE.
Then, transfer the cookies to a wire cooling rack and cool completely. Serve.