Make the Cake: 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 3 minutes, until frothy and dark yellow. Beat in sugar, coffee or water, and vanilla extract.
Whisk together cocoa, salt, baking powder, 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 10-15 minutes. You’ll know it’s done because if you lightly poke the top with your fingertip it will slightly bounce back.
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 (or you can wrap it overnight).
Make the Filling: beat heavy whipping cream in an electric mixer fitted with the whisk attachment. (You can also use a hand mixer, but it will take longer.) Slowly add in powdered sugar and vanilla during beating. Beat until whipped cream forms. Stir in crushed Oreos, reserving a tablespoon or two for garnish.
Assemble Cake: once the cake has cooled, unroll it carefully. Spread the whipped cream on the cake, leaving 1” without filling at either end. Re-roll cake, scooping out any filling that spills out as you roll. Cover with plastic wrap and chill for at least one hour before frosting. If you have leftover whipped cream, you can use it for topping, or top it like I did, see next step.
Make the topping: place chocolate chips and heavy whipping cream in a microwave safe measuring cup or bowl. Heat on high power for 60-90 seconds or until the cream is hot, then whisk until smooth. Let cool for 10 minutes.
Place cake roll on a wire rack set over a cookie sheet. Pour the ganache over the cake evenly. Top with remaining crushed cookies. Chill until set.
Note: The cake should stay chilled until right before serving or the whipped cream filling will get warm and it will be hard to slice.