Preheat the oven to 180°C. Grease and line a 20 cm round cake tin with parchment paper.
In a large bowl, mix 200 grams of all-purpose flour, 200 grams of sugar, 75 grams of cocoa powder, 1 1/2 teaspoons of baking powder, and 1 1/2 teaspoons of baking soda.
In another bowl, whisk together 240 ml of milk, 120 ml of vegetable oil, 2 large eggs, and 2 teaspoons of vanilla extract. Gradually add the wet ingredients to the dry ingredients, mixing until well combined.
Slowly pour in 240 ml of boiling water, stirring 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, then transfer to a wire rack to cool completely.
To prepare the chocolate truffle frosting, heat 400 grams of chopped dark chocolate and 400 ml of heavy cream in a double boiler over low heat, stirring until the chocolate is melted and the mixture is smooth. Remove from heat and let it cool to room temperature.
Once the frosting has cooled, whisk it until it becomes thick and spreadable. Spread the frosting evenly over the cooled cake, covering the top and sides.
Decorate the cake with chocolate shavings or cocoa powder, if desired. Refrigerate for at least 1 hour before serving.