Preheat your oven to 180°C. Grease and line a 20 cm round cake tin with parchment paper.
In a large mixing bowl, combine 200 grams all-purpose flour, 200 grams sugar, 75 grams cocoa powder, 1 1/2 teaspoons baking powder, and 1 1/2 teaspoons baking soda.
In another bowl, whisk together 240 ml milk, 120 ml vegetable oil, 2 large eggs, and 2 teaspoons vanilla extract. Gradually add the wet ingredients to the dry ingredients, mixing until well combined.
Slowly pour in 240 ml boiling water, stirring continuously until the batter is smooth. Pour the batter into the prepared cake tin.
Bake for 30-35 minutes, or until a toothpick inserted into the center of the cake comes out clean. Allow the cake to cool in the tin for 10 minutes before transferring it to a wire rack to cool completely.
Once the cake has cooled, crumble it into small pieces. In a separate bowl, prepare 400 grams of chocolate ganache by melting 200 grams of dark chocolate and mixing it with 200 ml of warm heavy cream.
In clean glass jars, layer the crumbled cake and chocolate ganache, starting with a layer of cake, followed by a layer of ganache, and repeating until the jar is full. Finish with a layer of ganache on top.
Refrigerate the jars for at least 1 hour before serving. Optionally, garnish with whipped cream, chocolate shavings, or fresh berries.