Let’s create “The Most Amazing Chocolate Cake”! First, prepare your oven and pan. Preheat the oven to 170°C (340°F – note this is slightly lower than typical 350°F/180°C). Grease one large, deep cake pan (e.g., 9 or 10-inch round, 3 inches deep, or a 9×13 inch pan) very well. Line the bottom with parchment paper and grease the parchment too. Set aside.

Begin the unique cake batter process. In the bowl of your stand mixer fitted with the whisk attachment, combine the room temperature eggs, sugar, salt, and vanilla extract. Whip on medium-high speed for several minutes (potentially 5-8 minutes) until the mixture is very airy, light in color, significantly increased in volume, and somewhat foamy – almost like ribboning batter for a sponge cake. This step is crucial for the cake’s texture.

Switch to the paddle attachment (or continue on low speed, or by hand gently). Add the room temperature sour cream and the oil to the whipped egg mixture. Mix slowly on low or medium-low speed just until the sour cream and oil are absorbed and combined. Do not overmix or deflate the airy egg base too much.

In a separate large bowl, sift together the all-purpose flour, cocoa powder, and baking soda. Add these sifted dry ingredients to the wet mixture in the mixer bowl. Mix on the slowest speed (or fold gently by hand) just until almost uniform – stop when there are still a few streaks of flour visible.

Carefully pour in the lukewarm water (or coffee). Mix again on the slowest speed (or gently whisk/fold by hand) only until you achieve a completely uniform, smooth batter. Scrape the bottom and sides to ensure everything is incorporated, but avoid overmixing. The batter might seem relatively thin.

Pour the finished batter into your single prepared deep cake pan. Bake in the preheated 170°C (340°F) oven for 50-60 minutes. This is a long baking time due to the large single layer; check it carefully. The cake is done when it appears quite risen (“swollen”), feels steady to a gentle touch in the center (not jiggly), and a wooden skewer inserted into the very center comes out with moist crumbs attached (not wet batter).

Once baked, let the cake cool completely in the pan on a wire rack. This may take several hours due to its size. Do not attempt to remove or slice it while warm.

Once the cake is completely cool, carefully run a knife or spatula around the edges and invert it onto a large plate or cutting board. Remove the parchment paper. Using a long, sharp serrated knife (like a bread knife) and a steady hand, carefully slice the cake horizontally into two equal layers. If the top is domed, you can level it first before slicing horizontally. Set the layers aside gently.

Prepare the Chocolate Ganache. Finely chop the dark chocolate and place it in a medium heatproof bowl. Pour the heavy whipping cream into a small saucepan and heat it over medium heat just until it comes to a simmer (bubbles forming around the edges). Do not let it boil vigorously. Immediately pour the hot cream over the chopped chocolate. Let it sit undisturbed for 3-5 minutes to allow the heat to soften the chocolate.

Gently whisk the mixture, starting from the center and working outwards, until the chocolate is completely melted and the ganache is uniform, smooth, and shiny.

Now, the crucial cooling step: Let the ganache cool completely at room temperature, stirring occasionally, for 4-5 hours (or possibly longer depending on room temp), until it thickens to the consistency of a thick, soft paste – like peanut butter or very soft frosting. It needs to be firm enough to hold its shape but still spreadable. To speed this up, you can place it in the refrigerator, but you must stir it vigorously every 10-15 minutes to ensure it cools evenly and doesn’t harden too much on the edges. Achieving this perfect spreadable consistency is key.

Assemble the cake. Place the bottom layer of the cooled, split cake onto your serving plate or cake stand. Scoop about one-third of the cooled, thickened ganache onto the center of the layer. Using an offset spatula or palate knife, spread the ganache evenly over the cake layer, right to the edges. (If adding optional nuts/coconut, fold them into this portion of ganache before spreading).

Carefully place the second cake layer on top. Use almost all of the remaining thickened ganache to frost the top and sides of the cake. Apply a generous layer and smooth it as desired using your offset spatula. Ganache frosting can be smoothed nicely or left with some texture.

Transfer the small amount of remaining ganache into a piping bag fitted with a 1 cm serrated piping tip (like a large star or shell tip). Pipe decorative borders, rosettes, or shells on the top edge or surface of the cake as desired.

Serve the cake at room temperature for the best texture (ganache will be firm if cold). Let it sit out for about an hour if refrigerated before serving.