In large bowl beat eggs & sugar, 5-10 minutes, or until thick & lightly yellow. Reduce speed to low, add vanilla & cocoa mixture. Mix just until combined. Slowly pour into prepared dish. Set dish into larger pan. Add hot tap water half way up the side of the dish.
Bake exactly 1 hour; a toothpick inserted 2" from side will come out clean. The center will appear very under cooked.
Cool completely. To make ahead wrap; refrigerate up to 3 days. To serve bring to room temperate and serve with ice cream, if desired.