To Make the Cake:

1. Preheat your oven to 170°C (340°F). Grease a round cake pan and line the bottom with parchment paper.

2. In a stand mixer with a whisk attachment, whip the eggs, sugar, salt, and vanilla extract until the mixture is light and airy.

3. Add the sour cream and vegetable oil. Mix on medium speed until well combined.

4. Sift the flour, cocoa powder, and baking soda into the bowl. Mix gently until the batter is nearly smooth.

5. Gradually pour in the lukewarm water while mixing, and continue mixing until the batter is fully combined and smooth.

6. Pour the batter into the prepared cake pan.

7. Bake for 50 to 60 minutes, or until the cake is set and a skewer inserted comes out with moist crumbs.

8. Let the cake cool completely in the pan. Once cooled, remove from the pan and slice horizontally into two even layers.

To Make the Ganache:

1. Place the chopped dark chocolate in a heatproof bowl.

2. Heat the cream in a saucepan or microwave until just boiling, then pour it over the chocolate.

3. Let it sit for a minute, then stir until smooth and glossy.

4. Allow the ganache to cool at room temperature for 4 to 5 hours, or refrigerate and stir occasionally until it thickens to a spreadable consistency.

To Assemble the Cake:

1. Place the bottom cake layer on a serving plate.

2. Spread one-third of the ganache evenly over the cake.

3. Top with the second cake layer.

4. Cover the top and sides of the cake with the remaining ganache.

5. Pipe any extra ganache over the top using a piping bag with a serrated tip for decoration.

6. Serve the cake at room temperature for the best texture.

7. Store leftovers in an airtight container for up to one week. Let it come to room temperature before serving if chilled.