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.

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.

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.

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.

Then, transfer the cookies to a wire cooling rack and cool completely. Serve.