Preheat your oven to 350°F (175°C). Grease and line two 9-inch round cake pans with parchment paper.

In a large mixing bowl, combine the flour, sugar, cocoa powder, baking powder, baking soda, and salt. Whisk until well combined.

Add the egg, milk, vegetable oil, and vanilla extract to the dry ingredients. Mix on medium speed for about 2 minutes until smooth.

Carefully stir in the boiling water. The batter will be thin, which is normal.

Pour the batter evenly into the prepared cake pans. Bake for 30-35 minutes or until a toothpick inserted in the center comes out clean.

Once baked, remove from the oven and let the cakes cool in the pans for 10 minutes. Then, transfer to a wire rack to cool completely.

Once the cakes are completely cooled, remove them from the pans. Place one layer on a serving platter.

Spread the softened vanilla ice cream evenly over the first layer of cake. Use a spatula to smooth it out.

Place the second layer of cake on top of the vanilla ice cream. Spread the softened chocolate ice cream over this layer.

Cover the cake with plastic wrap and freeze for at least 4 hours or until the ice cream is firm.

In a double boiler or microwave-safe bowl, heat 3/4 cup of heavy cream until it just begins to simmer.

Remove from heat and add the chopped chocolate. Let it sit for 5 minutes, then stir until smooth.

If the ganache is too thick, add a little more cream until you reach the desired consistency.

Once the ice cream cake is firm, remove it from the freezer. Pour the chocolate ganache over the top, allowing it to drip down the sides.

Top with whipped cream and chocolate shavings if desired. Return to the freezer for another 30 minutes to set the ganache.

Slice and serve the cake directly from the freezer for the best texture.