In a mixing bowl, combine heavy cream, evaporated milk and salt. With a stand mixer, beat until stiff peaks form gradually increasing speed to high, as mixture thickens. Stir sweetened condensed milk and chocolate syrup together in a bowl until it is mixed well. Slowly drizzle in sweetened condensed milk/chocolate syrup mixture starting mixer speed at low and gradually increasing it to high. Beat on high speed until stiff peaks form. Add vanilla extract. Beat until it is well blended, maintaining stiff peaks. Spread one-quarter ice cream on the bottom of a freezer-safe container. Scatter 1/3 cup chocolate fudge chunks on top, distributing evenly. Spread one-quarter ice cream evenly over the chocolate fudge chunks. Scatter 1/3 cup chocolate fudge chunks on top, distributing evenly. Spread one-quarter ice cream evenly over the chocolate fudge chunks. Scatter 1/3 cup chocolate fudge chunks on top, distributing evenly. Spread remaining one-quarter ice cream evenly over the top of the chocolate fudge chunks. Gently swirl the ice cream with a knife to move and separate the chocolate fudge chunks. Scatter ½ cup chocolate fudge chunks over the top layer of ice cream, distributing evenly. Cover tightly. Freeze until firm and completely solid, about 8-10 hours.
In saucepan, whisk cocoa powder, sugar, water and salt. Bring to a rolling boil over medium heat. Boil for 1 minute, stirring constantly. Remove from heat. Stir in vanilla extract. Cool completely.
Chocolate Fudge Chunks:
Line an 8x8-inch pan with foil. Set aside. Add all ingredients into a double-boiler. Stir and melt until the chocolate is melted and completely smooth. Pour in an even layer into prepared pan. Refrigerate or freeze until set. Remove foil from large chocolate bar and place on a cutting board. While still cold, cut into ½-inch cubes. Keep refrigerated or frozen.