In a large bowl, combine eggs, granulated sugar, melted chocolate, oil, baking powder, and vanilla. Beat with an electric mixer on medium speed until combined, scraping side of bowl occasionally. Gradually beat in as much of the flour as you can with the mixer. Using a wooden spoon, stir in any remaining flour. Divide dough in half. Cover and chill for 2 to 24 hours or until dough is easy to handle.

Preheat oven to 375 degrees F. Lightly grease a large cookie sheet; set aside. Place demerara sugar in a small bowl. Shape one portion of dough into 1/2-inch balls. Shape the remaining portion of dough into 1-inch balls. Roll balls in demerara sugar to coat generously. Place balls 1 inch apart on prepared cookie sheet.

Bake small cookies in the preheated oven about 8 minutes or until edges are set and tops are dry. Bake large cookies about 10 minutes or until edges are set and tops are dry. Do not overbake cookies. Transfer cookies to a wire rack; let cool. (Cookies will deflate slightly upon cooling.) Makes about about 72 small and 36 large cookies.

To Store: Layer cookies between waxed paper in an airtight container; cover. Store at room temperature for up to 3 days or freeze for up to 3 months.