Preheat the oven to 350-degrees F. Line a baking pan with parchment paper.
In the bowl of an electric mixer fitted with the paddle attachment, beat the eggs. Add in the inside of the vanilla beans, vanilla extract and melted butter.
Add cake mix and flour. Mix to combine.
Divide the dough in half. Make two logs, about 12″ long by 2″ wide on the baking sheet. Bake for 30-35 minutes.
Remove the baked logs to a cutting board and allow to cool for 15 minutes. Cut the logs into 1″ slices using a serrated (bread) knife.
Place the slices back on the baking sheet with the cut side down. Bake an additional 10-15 minutes until the cookies are firm. Cool completely.
In a small bowl, combine the confectioners' sugar, vanilla extract and coffee.
Dip the bisccotti in the coffee glaze and set out on parchment until the glaze hardens. Serve with a hot cup of coffee, or package in glassine bags as gifts.