Place a cooking stone in the freezer, preheat the oven to 350°F, and grease a 7-inch springform pan. For the chocolate cake, whisk together all of the ingredients at room temperature. Once a smooth batter forms, pour it into the greased springform pan, transfer the springform pan to the oven, and bake at 350°F for 1 hour. Let the cake cool, then cut off the topmost layer so that the top surface of the cake is even. Cut the rest of the cake in half lengthwise so that you end up with 2 even cake layers and set them aside for later.
For the shortbread, knead together all of the ingredients by hand until a smooth dough forms. Wrap the dough in plastic wrap and refrigerate for 1 hour. Preheat the oven to 325°F. Remove the dough from the fridge and roll it out until it is ½-inch thick. Cut the rolled out dough into a circle 7 inches in diameter and poke small holes in the surface with a fork. Place the shortbread on a baking tray lined with parchment paper, transfer the baking tray to the oven, and bake at 325°F for 40 minutes. Let the shortbread cool and set it aside for later.
For the caramel sauce, heat the heavy cream on the stove until it comes to a rapid boil, then remove it from the heat and set aside. Heat the corn syrup on high heat in a separate saucepan and gradually add in the sugar. Once the caramel sauce has started to take on a nice brown color, begin to stir in the warmed heavy cream until it's fully incorporated. Let the sauce cool down to about 95°F, then stir in the butter. Transfer the caramel sauce to the refrigerator and let cool.
For the Twix ice cream, remove the cooking stone from the freezer, put half of the ice cream on it, and add some Twix bars and soft caramels. Chop everything up and mix it together thoroughly, then scoop the Twix ice cream into a deep 7-inch springform pan. Spread the ice cream layer evenly over the base, then pour caramel sauce over the ice cream layer.
Place 1 layer of chocolate cake on top of the caramel syrup and then put the shortbread on top of the chocolate cake layer.
Prepare the other half of Twix ice cream and spread it evenly over the shortbread. Smooth out the ice cream layer and top it with another layer of caramel sauce.
Place the second layer of chocolate cake on top of the caramel sauce. Cover the springform pan with a plate and flip the cake over so that the Twix ice cream layer is on top. Remove the cake from the springform pan, transfer the plate to the freezer, and freeze for 2 hours.
For the chocolate ganache, dissolve the gelatin powder in water and set aside. Heat the water, sugar, and corn syrup on the stove until it reaches 225°F, stirring continuously. Combine the semi-sweet chocolate chips, sweetened condensed milk, and gelatin mixture in a large heat-resistant bowl, then pour the boiling syrup mixture into the bowl. Use a hand blender to emulsify the mixture until it becomes smooth and creamy. Let the ganache cool to 85°F, pour it over the cake, and let it set.
Pipe chocolate frosting rosettes on top of the cake and top with Twix pieces. Finally, use icing to write a special message in the center.