Preheat the oven to 325F and check that a deep 9x13” pan will fit into a roasting pan, place a kitchen hand towel in the bottom of the pan and heat up some water for the water bath.
Place 1 cup of sugar into a non stick medium sized pan, melt on medium heat, do not stir, shake the pan to move the sugar around occasionally, cook till dark golden brown and all the sugar is dissolved. Quickly pour the hot sugar into the bottom of your 9x13” pan and swirl around to spread the caramel out to all the corners, it helps to have someone else pour while you swirl.
Heat the milk with cinnamon sticks till steaming in a large pot, let steep for at least 10 minutes until the cinnamon stick starts to uncurl.
In a separate bowl whisk the 8 eggs and reaming ¾ cup of sugar, slowly pour the warm milk into the egg mixture stirring constantly, add vanilla extract.
Pour the custard through a mesh strainer into the prepared caramel lined dish and set aside.
Chocolate chiffon cake
In a small bowl combine cocoa powder and hot coffee, stir till smooth, set aside and let cool.
In a separate large bowl whisk together the dry ingredients, flour, sugar, baking soda and salt.
Separate the eggs, the whites into a large clean mixing bowl to whip and the egg yolks into the cocoa mixture along with the oil and vanilla.
Add the cocoa and egg yolk mixture to the dry ingredients and mix till almost combined, it’s okay if there are lumps, you’ll be folding egg whites into it soon.
Whip the egg whites with the cream of tartar until they form stiff peaks and fold into the cake batter until there are no white streaks.
Gently pour the cake on top of the custard, it floats! Place the cake pan in the roasting pan and put it into the preheated oven, pour the hot water into the roasting pan so it comes up about half way on the cake pan.
Bake at 325F for 40-50 minutes or until a tooth pick inserted half way comes out clean, you want to make sure you don’t touch into the custard layer because it may give you a false reading. Remove the cake pan from the water bath, slide a knife around the edges of the cake to release it, it’ll jiggle a little because of the custard layer hidden underneath, chill at least 6 hours.
When ready to serve run a knife around all the edges down to the bottom of the pan, place a large serving platter upside down on the cake and flip the whole thing over.