There is no one definitive recipe for Hershey's dark chocolate cake. However, a quick search online will reveal a number of recipes that claim to be the original or definitive recipe.

COMBINE ALL DRY INGREDIENTS IN A LARGE BOWL.
ADD ALL OTHER INGREDIENTSEXCEPT FOR THE BOILING WATER.
BEAT UNTIL WELL MIXED, ABOUT 2 MINUTES ATMEDIUM SPEED.
STIR IN BOILING WATER (BATTER WILL BE THIN).
POUR INTOGREASED PAN (EITHER 1, 9 X 13 OR 2, 9 ROUND).
BAKE AT 350 DEG F FOR 30TO 35 MINUTES FOR ROUND PANS OR 35 TO 40 FOR SHEET PAN.
COOL 10 MINUTES INPAN, THEN REMOVE TO WIRE RACK AND COOL COMPLETELY.
Ingredients
Directions
COMBINE ALL DRY INGREDIENTS IN A LARGE BOWL.
ADD ALL OTHER INGREDIENTSEXCEPT FOR THE BOILING WATER.
BEAT UNTIL WELL MIXED, ABOUT 2 MINUTES ATMEDIUM SPEED.
STIR IN BOILING WATER (BATTER WILL BE THIN).
POUR INTOGREASED PAN (EITHER 1, 9 X 13 OR 2, 9 ROUND).
BAKE AT 350 DEG F FOR 30TO 35 MINUTES FOR ROUND PANS OR 35 TO 40 FOR SHEET PAN.
COOL 10 MINUTES INPAN, THEN REMOVE TO WIRE RACK AND COOL COMPLETELY.