Preheat oven to 350°F. Spray or grease a jellyroll pan (helps keep the parchment in place), then line the jellyroll pan with parchment paper and grease or spray the parchment as well. Set aside.
In the bowl of your electric mixer (fitted with the whisk attachment), beat the eggs for 2 minutes on high speed until fluffy and pale in color. Gradually add the granulated sugar. Beat 2 more minutes on medium speed. Scrape down the sides of the bowl as needed.
Add the cocoa powder, flour, baking soda, salt, hot water, and vanilla extract. Mix on low speed for about 1 minute or until just combined. Pour batter into the jellyroll pan and use a spatula to spread the batter into an even layer. Bake for 18-20 minutes, or until a toothpick entered in the center comes out clean. Be careful not to overbake the cake.
While the cake is baking spread a thin dishtowel onto a flat surface. Generously dust the towel with powdered sugar. Remove cake from oven then turn the cake onto the prepared towel. Peel off the parchment paper.
Starting with the narrow end, immediately roll the cake and towel together. Let the cake sit until cool.
Once cool, unroll cake and spread the softened ice cream over the surface of the cake. I use about 1/2 of a half gallon of ice cream. You don't want to add too much ice cream, otherwise it will just seep out when rolling it up.
Re-roll cake without the towel. (See notes). Cover with aluminum foil or plastic wrap and place in the freezer. Let it freeze for 4-6 hours, but preferably overnight.
Remove from freezer, dust the cake roll with powdered sugar. Slice, and serve with hot fudge and any other toppings you'd like!