Prepare the cake layers first. Preheat the oven to 350F/177C and line the bottom of 2, 8-inch (20-cm) pans with parchment paper. In a large mixing bowl, cream together the softened butter, sugar and vanilla for a few minutes, until smooth and creamy. Add the eggs, one at a time, mixing well after each addition. Pour in the milk but do not mix.
In a separate bowl, combine the dry ingredients: flour, baking powder and salt. Sift the dry ingredients into the batter and mix by hand, just until the dry ingredient are incorporated. Separate the batter in half. Into the second half, add the cocoa powder and melted chocolate, then mix until well combined. Pour the batters into the prepared pans. Bake in preheated oven for 30 to 35 minutes, until a toothpick inserted into the center comes out clean. Allow the layers to cool completely, then level the tops if needed and cut in half with a long, serrated knife.
Once the layers are cooled, prepare the cheesecake filling. In a large mixing bowl, beat the cream cheese, vanilla and sour cream for 3 to 4 minutes, until the mixture is smooth. Scrape down the sides of the mixing bowl to ensure no clumps of cheese remain. Add the sweetened condensed milk and mix again for a minute.
In a small ramekin, prepare the gelatin mixture. Combine the unflavored gelatin and water, stirring until the gelatin is absorbed. Microwave the mixture for 30 seconds, stirring every 10 seconds, until the gelatin is dissolved. Pour the hot gelatin directly into the filling and mix it in right away. Divide the batter into two separate mixing bowls.
Into one mixing bowl, add the melted dark chocolate; into the second bowl, add the melted white chocolate. Use a mixer or whisk to mix the chocolate into the batter.
Assemble the cake in an 8-inch springform pan (or corresponding size pan). Begin with the chocolate cake layer. Soak the first half generously with chocolate sauce (or melted chocolate) and add a layer of sliced strawberries. Top with the second half and repeat the process. If using an acetate cake collar, insert it into the pan, then pour in the chocolate cheesecake filling. Spread the filling evenly to the edges, then top with the first vanilla cake layer.
Soak the vanilla cake layer with caramel sauce, then add a layer of strawberries and repeat. Add the white chocolate cheesecake filling on top last and use an offset spatula to level the top. Place the cake into the refrigerator and allow it to set for at least 6 hours, or best overnight.
Once cake is set, use a cake spatula to gently transfer the cake onto a stand. Prepare a batch of chocolate ganache (recipe link above) and pour it over the top. Use a small spatula to nudge the chocolate down the sides. Allow the chocolate to set for about 15 minutes, then add the strawberry whipped cream (optional). You can also use regular whipped cream for this recipe. Garnish with additional strawberries, if desired.
Keep cake refrigerated until ready to serve; it can be left at room temperature for up to 2 hours.