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Ingredients
- 1 (12 ounce) can Coke (or other cola), divided
- 2 (4 ounces each) sticks unsalted butter (each stick = 1/2 cup), divided, at room temperature
- 1 (1 ounce) square semisweet chocolate
- 1 cup miniature marshmallows (measured by volume not weight)
- 1/2 cup shortening (I used butter flavor Crisco) (measured by volume)
- 1/2 cup canola oil or sunflower oil
- 3 tsp vanilla extract, divided
- 2 cups granulated white sugar or caster sugar
- 2 large eggs
- 3/4 cup milk (I used 2% fat)*
- 3 Tbsp powdered buttermilk*
- 1 tsp baking soda
- 1 1/2 tsp baking powder
- 1/2 tsp salt
- 2 1/3 cups White Lily all-purpose flour
- 1 1/4 cups unsweetened dark chocolate cocoa powder, divided
- 1/4 cup chocolate syrup (I used Fox's U-Bet)
- 2 cups powdered sugar or icing sugar
Preparation
Step 1
Before you begin, open your oven and arrange baking racks so that one of them is set near top, making sure there is plenty of room on that top shelf for your pan and for cake to rise a bit. Normally cakes are baked in center of oven, but not this one. Preheat your oven to 350 degrees. Grease and flour 9x13" rectangular sheet cake pan. You will also need small saucepan, whisk, electric mixer, and 3 mixing bowls.
Measure out just 1 cup Coke and just 1 stick of butter and place along with square of semisweet chocolate into small saucepan. Set remaining cola aside for now, and place other stick of butter in medium mixing bowl, setting it aside to come to room temperature.
Meanwhile, bring mixture in your saucepan to boil, stirring with whisk or slotted spoon often. As soon as it boils, add mini marshmallows, stir to coat, lowering heat a bit to prevent a boil-over. Continue to stir until everything has fully melted and blended together, and there are no longer any white streaks remaining from the marshmallows. It should look shiny and wet, like unset fudge. Set this fudge mixture aside to cool a bit (I let mine sit for about 5 minutes, then poured it into a plastic bowl and popped it into the fridge for about another 5 minutes while I continued with next step).
In a large mixing bowl combine the shortening, oil, and just 2 tsp of the vanilla. Add the granulated sugar and mix well. Add in both eggs and the milk and beat well, using an electric mixer, until light and fluffy. Scrape any batter that is creeping up the sides of the bowl with a spatula, as needed.
In yet another mixing bowl (last one I promise!), combine the buttermilk powder, baking soda, baking powder, and salt. Set a mesh strainer/sieve over the top of the bowl and add the flour, shaking the strainer so that the flour sifts down into the bowl. If you happen to have a flour sifter, you can use that instead, but a mesh strainer works just fine. Measure out just 3/4 cup of the unsweetened cocoa powder and sift that through the sieve as well. Remove the sieve and give the mixture a quick stir.
Add half of the flour mixture into the shortening & egg mixture, beating until smooth.
Remember your fudge mixture you have cooling? Give that a quick stir and then add just a bit of it to the shortening mixture and beat well. Continue adding the fudge in small amounts until all of it has been beaten in and well combined. The reason you are adding it slowly is to prevent the still somewhat warm mixture from scrambling your eggs.
Add the other half of the flour mixture now, mixing until combined and then for another 4 minutes. Set a timer. You are trying to incorporate air into your batter, so no skimping on the time here. Your batter should be thick and smooth.
Pour the cake batter into your prepared pan and pop it into the preheated 350 F oven to bake on the TOP rack. Bake for 35-40 minutes, or until a toothpick poked into the center of the cake comes out with no streaks on it. Do not overbake! Set the cake onto a cooling rack to cool somewhat. You will still want it to be a bit warm when you add the fudge icing, but wait long enough for it to no longer be so very hot that your icing just melts completely upon contact. Before you walk away, take your toothpick and poke a bunch of holes all over the surface of the cake.
Remember the bowl with the stick of butter in it from way back in the beginning? By now it should be nice and soft. Go grab the rest of that can of coke and measure out about 1/3 cup. Add that to the butter, along with 1 tsp vanilla, and the remaining 1/2 cup unsweetened cocoa powder. Add the chocolate syrup and mix well until everything is smooth. Now add in 1 cup of the powdered sugar and blend well, then add the remaining 1 cup powdered sugar. The icing should be shiny, smooth, and a bit gloopy, not stiff. It should not be watery, but more like the consistency of thick hot fudge sauce. If it is too thin, add a bit more powdered sugar, or if it seems a bit too dry, add a little more cola.
Pour this entire mixture over the warm cake and spread evenly. Allow this to sit long enough to set up a bit, about 20-30 minutes, roughly. Some of the fudgey icing will ooze into your toothpick holes and you need to give it time to do that. The surface will also take on a sheen and harden ever so slightly. Serve with a scoop of vanilla bean ice cream on the side while the cake is still a little warm, if desired.
*NOTE: If you don't have buttermilk powder, you may instead use 3/4 cup buttermilk instead of the milk and buttermilk powder. Or, you can make a buttermilk substitute by placing 2 tsp lemon juice into a measuring cup, then adding enough milk to fill 3/4 cup, and then allowing that to sit for 5 minutes to thicken. You will not need to make any adjustments to the dry ingredients.