Separate eggs, discarding 3 of the yolks or saving for another use. Let eggs stand at room temperature 30 minutes. Preheat oven to 325 degrees F. Dissolve espresso in water; set aside.
In large bowl stir together flour, sugar, baking powder, and salt; make well in center. Add oil, the 5 egg yolks, dissolved espresso, and vanilla. Beat on low until moistened; beat on medium-high 4 to 5 minutes or until satin smooth. Stir in grated chocolate.