Preheat your oven to 350°F (175°C). In a large mixing bowl, combine the cake mix, eggs, chocolate syrup, cold water, vegetable oil, vanilla paste, and kosher salt. Beat on medium speed for about 2 minutes until smooth.
Pour the batter into a greased 9x13 inch baking pan. Bake for 30-35 minutes or until a toothpick comes out clean. Let it cool for 15 minutes, then transfer to a wire rack to cool completely.
In a double boiler or microwave-safe bowl, combine bittersweet chocolate, water, corn syrup, and a heavy pinch of salt. Heat gently, stirring until melted and smooth. Stir in vanilla paste and set aside to cool slightly.
Once the cake is cooled, cut it in half horizontally. Place one layer back in the pan, spread half of the ice cream, and pour half of the hot fudge sauce over it.
Place the second layer of cake on top, spread the remaining ice cream, and pour the rest of the hot fudge sauce on top.
Spread whipped cream over the fudge sauce and garnish with cherries. Cover and freeze for at least 4 hours or until set.