To make the ice cream custard (day one):

1. Make sure your ice cream maker drum has been thoroughly frozen according to the manufacturer’s instructions. Place the dark chocolate shavings and quartered cherries in the refrigerator.
2. In a medium pot over medium heat, combine the milk, cream, and sugar. Stir until the sugar is fully dissolved and the mixture is warm but not boiling. Stir in the vanilla extract.
3. Slowly pour the whisked eggs into the warm cream mixture, stirring constantly so the eggs don’t scramble. Continue cooking over medium heat, stirring constantly, until the custard thickens enough to coat the back of a spoon, about 10 to 15 minutes. It should look glossy and feel slightly thicker than heavy cream.
4. Remove from heat and let cool completely. Cover and refrigerate overnight, at least 12 hours. This cold rest is essential for a smooth, creamy texture.

To churn the ice cream (day two):

1. Pour the chilled custard into your ice cream maker and churn according to the manufacturer’s instructions. When the ice cream is thick and holds its shape but is still soft enough to stir, fold in the cold cherries and dark chocolate shavings in batches until evenly distributed.
2. Transfer the ice cream to the freezer for about 30 minutes to firm up slightly. This recipe makes double the ice cream you need for the sandwiches — save the other half in a bread tin or freezer-safe container with plastic wrap pressed against the surface.

To make the chocolate cake (day two):

1. Preheat the oven to 350°F. Grease a 9×13-inch cake pan and line it with parchment paper.
2. In a stand mixer fitted with the paddle attachment, cream the butter and sugar together until light and fluffy, about 2 to 3 minutes. Add the eggs and vanilla and mix until just combined.
3. In a separate bowl, whisk together the flour, cocoa powder, baking powder, and salt.
4. With the mixer on medium-low, slowly add the dry ingredients to the butter mixture. Mix until just incorporated — do not overmix. Fold in the dark chocolate shavings by hand.
5. Pour the batter into the prepared pan and spread it into a thin, even layer using an offset spatula or the back of a spoon. Bake for 12 to 15 minutes, until a toothpick inserted in the center comes out clean and the cake springs back lightly when touched.
6. Let the cake cool in the pan for 10 minutes, then carefully transfer to a wire rack to cool completely. Once fully cooled, cut the cake in half widthwise. Wrap each piece in plastic wrap and freeze until the ice cream is ready.

To assemble (day two, then freeze overnight):

1. Unwrap both cake pieces and place one piece flat on a large sheet of plastic wrap. Working quickly, spread about half of the ice cream in an even layer over the cake. Place the second piece of cake on top and press down gently.
2. Wrap the whole sandwich tightly in plastic wrap and freeze overnight until completely solid.

To slice and serve (day three):

1. Unwrap the frozen sandwich and use a large, sharp knife to cut into 8 even bars. If the knife sticks, run it under hot water and wipe dry between cuts. Serve immediately or wrap each bar individually in parchment paper and store in the freezer.