Preheat your oven to 350°F (175°C). In a large mixing bowl, combine all-purpose flour, cocoa powder, baking powder, baking soda, salt, and granulated sugar. In a separate bowl, whisk together eggs, milk, and vegetable oil. Gradually add the wet ingredients to the dry mixture, stirring until a smooth batter forms. Pour the batter into a greased 9-inch round cake pan and bake for 30-35 minutes, or until a toothpick inserted into the center comes out clean. Allow the cake to cool completely.

In a heatproof bowl, melt white and semi-sweet chocolate together with butter over a double boiler or in the microwave in 30-second intervals, stirring until smooth. In another bowl, whip heavy cream until stiff peaks form, then gently fold in the melted chocolate mixture. In a small bowl, dissolve gelatin in water, heat until dissolved, and mix it into the chocolate-cream blend until well combined.

Once the cake base has cooled, carefully remove it from the pan and place it on a serving plate. Line the sides of a springform pan with parchment paper for easy removal, then put the cooled cake at the bottom. Pour the chocolate mousse over the cake, ensuring it's evenly spread. Refrigerate the entire setup for at least 4 hours or overnight.

After the mousse has set firm, prepare the chocolate ganache by heating semi-sweet chocolate and heavy cream together in a small saucepan over low heat. Stir until the chocolate melts and the mixture is smooth and glossy. Carefully pour the ganache over the set mousse layer, allowing it to drizzle down the sides. Refrigerate again for about 30 minutes.

When ready to serve, run a knife around the edge of the springform pan and gently release the sides. Cut the cake into slices, showcasing the layered mousse and cake, and top each slice with fresh strawberries and optional chocolate curls. Serve chilled.