Preheat the oven to 350°F (175°C). Grease a 9-inch round cake pan and line the bottom with parchment paper.
Whisk together the flour, sugar, cocoa powder, baking powder, baking soda, and salt.
Add the eggs, buttermilk, vegetable oil, and vanilla. Mix until the batter is smooth.
Slowly add the hot water and mix until combined. The batter will be thin.
Pour the batter into the prepared pan and bake for 25 to 30 minutes, or until a toothpick inserted in the center comes out with a few moist crumbs.
Cool the cake in the pan for about 10 minutes, then transfer it to a wire rack and cool completely.
Let the vanilla ice cream soften until it is creamy and easy to spread, but not melted.
Gently fold the Baileys Irish Cream and chocolate chips into the softened ice cream.
Place the cooled cake into a clean 9-inch pan or springform pan. If necessary, trim the top so the cake is relatively level.
Spread the Baileys ice cream mixture evenly over the cake.
Cover tightly and freeze for at least 4 to 6 hours, preferably overnight.
For the topping, gently melt the chocolate with the heavy cream until smooth. Stir in the Baileys and let the mixture cool slightly.
Remove the frozen cake from the pan and spread the chocolate topping over the surface.
Garnish with whipped cream or chocolate shavings if desired.
Freeze for another 30 to 60 minutes, then let the cake sit at room temperature for 5 to 10 minutes before slicing.
