Chocolate Chiffon Cake:

Preheat oven to 350 degrees Fahrenheit (175 C). Let eggs stand at room temperature for 30 min. Line a jelly roll pan (10.5" x 15.5") with parchment paper. Do not grease the pan or the parchment paper. Prepare hot coffee, and mix 1/2 cup of hot coffee with 1/4 cup of cocoa powder. Mix well and let it cool.

In a large bowl, sift together all the remaining dry ingredients (excluding cocoa powder).
Add in the egg yolks, oil, vanilla extract, orange zest, as well as coffee/chocolate mixture. Beat with an electric mixer or by hand just until smooth and well blended.

In a separate bowl, beat 4 egg whites and 1/2 tsp cream of tartar on high speed until frothy. Gradually add in 1/3 cups sugar and beat until glossy stiff peaks are formed. Gradually and very gently fold in this meringue into cake mixture until very well combined. Pour this into the prepared jelly roll pan, and smooth the top with the spatula.

Bake for about 15 to 18 minutes or until a toothpick inserted into the center of the cake comes out clean. Dust the cake with some confectioner's sugar to prevent sticking. Place a rectangular piece of parchment paper that's bigger than the cake on top, and invert the cake onto the parchment paper and slowly remove the baking pan so that parchment paper is on top. Then slowly peel off the parchment paper.

While the cake is still warm, dust additional confectioner's sugar onto this side of the cake (to prevent cake from sticking), and roll the cake with the parchment paper along the short 10.5-inch side, place with the seam side down so it doesn't unroll, and let it cool to room temperature on a wire rack.

Chocolate Ganache:

Take 16 oz of high-quality bittersweet (or semisweet) chocolate (about 2 + 2/3 cups chocolate chips), and put it in a large heatproof bowl.

In a medium sized saucepan, add 1 cup of heavy cream, 1/4 cup of sugar and bring them to a boil on low-medium heat, while whisking, till the sugar has dissolved. When the mixture is smooth and slightly simmering (but not boiling), remove the saucepan from the heat.

Pour the hot heavy cream mixture over the 16 oz of bittersweet chocolate, and mix together to melt the chocolate. While the mixture is still hot, add 4 tablespoons of unsalted butter that's been cut into pieces, and an optional 1 tbsp of brandy, and whisk this into the mixture until it's smooth.

Continue stirring it till it cools and becomes a nice spreadable consistency. During the summer / on a hot day, it may be necessary to put the bowl in the fridge for the chocolate to become firm enough to spread.

Chocolate Curls:

Set up a double boiler over medium heat. Add in 2 oz of bittersweet chocolate and stir it around till it's all melted and smooth. Take the bowl off the heat, and let it cool for about 10 minutes. Keep the double boiler for later. Also put a sheet pan in the fridge for 10 minutes.

Take a sheet pan out of the fridge and place it upside down on the counter. Pour your tempered chocolate onto the cold sheet pan.

With a spatula, push the chocolate back and forth, spreading it into a thin layer. As you push and spread the chocolate back and forth, you'll see it firm up if your room is cold enough / during winter. You are done when the chocolate changes from being glossy and shiny to having more of a matte look.

During the summer / on a hot day, it is necessary to put the sheet pan with the thin layer of chocolate spread on it into the fridge for 20 - 30 minutes. Also, put your bench scraper in the freezer, so it's cold when it touches the chocolate.

When you think your chocolate is set enough, take the sheet pan out of the oven and your cold bench scraper, and at a 45-degree angle, scrape it with a pretty quick and confident motion. If the chocolate starts to crumble immediately, it means the chocolate is too cold, and let it warm up for 5 - 10 seconds, and try again.

If the chocolate just clumps up into a melted pile onto your scraper, then it means it's not cold / set enough, and needs to go in the fridge for another 10 minutes.

When the chocolate is just the right consistency, with a pretty quick and confident motion, the chocolate will form curls when you scrape it at a 45-degree angle. Especially in hot weather when chocolate warms up very quickly, this step can be very temperamental. And there's only a small (30 second - 1 minute) window when your chocolate is the right temperature / consistency that it forms curls. So, you might have to put the sheet pan back and forth in the fridge multiple times before you get all the curls you want.

Aim for 8 curls, but you may make as many curls as you'd like. Once you have 8 curls you're happy with, store your curls in the fridge, or even your freeze till you're ready to use them, as the curls may melt and lose their shape. If you made curls in multiple attempts, put the successful curls in the fridge immediately so it doesn't lose its shape.

Assembling the cake:

When the cake has cooled to room temperature and ganache / curls are ready, slowly and carefully unroll the cake.

Spread a thin layer of the chocolate ganache on the top surface of the cake, about 1/8" thick.

Slowly and carefully roll the cake up again, the same direction it was rolled before but this time without the parchment paper rolled into it.

Transfer the roll to your serving dish, with the seam-side down, so it doesn't unroll. Fill the gaps at the ends of the cake with chocolate. Then cover the outer surface of the cake with a thin layer of ganache, as a crumb coat. Smooth it out with a bench scraper, and let your cake rest in the fridge for 20 minutes for the ganache to harden a bit.

When your crumb coat has hardened a bit, apply a 2nd layer of ganache, about 1/8" thick on the outer surfaces. Smoothen it with a bench scraper. If you have an icing comb, you can create a pattern on the outside surface of the ganache at this point. Remember to save at least 3 tbsp of ganache frosting to make drizzles at the top of the cake at the end.

Place your 8 chocolate curls along the top of the roll. Place your cake in the fridge, while we work on the chocolate drizzle.

Put the remaining ganache back on the double boiler, and re-warm the chocolate so it returns to having a runnier consistency.

Transfer the ganache into a small Ziploc bag or disposable piping bag. Snip a very small hole in one corner.

Do some test drizzles the bowl it was in. If it's too runny, let it cool for a bit, and try again. The ganache will thicken as it cools. Drizzling ganache can be tricky, as sometimes it's too runny when too hot, or doesn't drizzle when too cool. You sort of have to estimate when it's the right consistency to create the drizzle effect that you want.

When the drizzles reach the consistency you want, drizzle it over your cake roll in a zig-zag, pattern.

Refrigerate for 2 hours to overnight for the cake to set. Leave out at room temperature for 2 to 3 hours before serving - for the chocolate ganache to soften a bit. Enjoy!