Preheat your oven to 350°F (175°C). In a large bowl, mix together the flour, sugar, cocoa powder, baking powder, baking soda, and salt. Add eggs, milk, oil, and vanilla. Beat on medium speed for 2 minutes. Stir in boiling water (batter will be thin). Pour into greased and floured cake pans.

Bake the Cake

Bake for 30-35 minutes or until a toothpick inserted in the center comes out clean. Cool in pans for 10 minutes, then remove from pans to cool completely.

Custard Preparation

Make the Custard

In a saucepan, combine milk, cream, and sugar. Heat until steaming. In a separate bowl, whisk egg yolks. Gradually add hot milk mixture to the yolks, whisking constantly. Return to saucepan and cook until thickened. Stir in cocoa and gelatin mixed with cold water. Chill until set.

Nutella Crunch Preparation

Prepare the Nutella Crunch

In a bowl, mix chopped hazelnuts, Nutella, melted butter, flour, and brown sugar until crumbly. Spread on a baking sheet and bake at 350°F (175°C) for 10-12 minutes until golden. Let cool, then break into pieces.

Espresso Ice Cream Preparation

Make the Espresso Ice Cream

In a bowl, whisk together cream, milk, sugar, espresso, vanilla, and salt. Pour into an ice cream maker and churn according to manufacturer's instructions until thick and creamy. Freeze until firm.

Assembly

Assemble the Cake

Once the cake has cooled, spread the custard evenly over the top. Sprinkle with Nutella crunch and serve with scoops of espresso ice cream.