Mix together oil, chocolate, sugar and vanilla. Stir in eggs one at a time, beating well after each addition.

Add flour and mix well (batter will be runny). Cover and refrigerate at least 3 hours.

Use a small or large cookie scoop (or shape into balls with your hands), and roll in a dish of the icing sugar. Place balls onto a parchment lined baking sheet.

Bake at 350°F for 10 to 18 minutes (depending on size of cookie), or until almost no imprint remains when cookie is lighted touched. Cool for 10 minutes, then move to cooling rack.