Preheat oven to 350°F (175°C) and grease a 9-inch springform pan.
Whisk flour, sugar, cocoa, baking powder, baking soda, and salt in a large bowl.
Add eggs, milk, oil, and vanilla; beat on medium speed for 2 minutes.
Stir in boiling water by hand; the batter will be thin.
Pour batter into the pan and bake for 30-35 minutes until a toothpick comes out clean.
Cool the cake completely in the pan.
Spread softened chocolate ice cream evenly over the cooled cake layer.
Cover and freeze for at least 3 hours or until the ice cream is firm.
Prepare ganache by heating heavy cream until simmering, then pouring over chopped chocolate; let sit for 5 minutes and stir until smooth.
Pour cooled ganache over the frozen ice cream layer and freeze for an additional 30 minutes before serving.