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 inserted comes out clean. Allow to cool completely in the pan.
While the cake is cooling, prepare the hot fudge sauce. In a double boiler or microwave-safe bowl, combine bittersweet chocolate, sweetened condensed milk, water, corn syrup, salt, and vanilla. Melt and stir until smooth, then set aside to cool slightly.
Once the cake is cool, spread the softened ice cream evenly over the cake.
Drizzle the warm hot fudge sauce over the ice cream, spreading it slightly with a spatula and swirling for a marbled effect.
Spread the whipped cream over the fudge layer and garnish with maraschino cherries.
Cover with plastic wrap and freeze for at least 2-3 hours before serving. Let sit for 10 minutes before cutting.
