Preheat oven to 350°F. Line a jelly roll (10x15”) pan with foil and spray with cooking spray (I like to use the spray with flour).
Beat eggs at high speed for 5 minutes, until frothy and dark yellow. Beat in sugar, water or coffee and vanilla extract.
Whisk together salt, baking powder, cocoa and flour. Stir into wet ingredients just until blended.
Spread in prepared pan. Batter will be in a very thin layer and you will need to use a wooden spoon or spatula to spread it to all the corners of the pan. Bake for 9-15 minutes or until it springs back when poked.
While the cake is baking, set a clean kitchen towel out on a large work surface. Sprinkle liberally with powdered sugar (about 1/4 cup). As soon as the cake comes out of the oven, turn it over on the kitchen towel sprinkled with powdered sugar. Remove foil carefully.
Working at the short end, fold the edge of the towel over the cake. Roll tightly, rolling up the cake into the towel. Let cool completely while rolled, at least one hour.
While the cake is cooling, place heavy cream and chocolate chips in a microwave safe bowl or measuring cup. Heat for about 45 seconds, then whisk until smooth. If the chocolate doesn’t want to melt, you can heat in additional 15 second increments until it will. Chill until the mixture is thick about 15-30 minutes. Once it's thick and chilled, beat it with a hand mixer until lighter in color and fluffier.
When you want to assemble the cake, unroll the roll carefully. Spread the frosting evenly over the top.Re-roll your cake, wrap tightly in plastic wrap and chill for about an hour before serving. Dust with powdered sugar and cocoa before slicing and serving.