Preheat the oven to 350°F (175°C). In a large mixing bowl, whisk together the flour, sugar, cocoa powder, baking powder, baking soda, and salt. Add the eggs, milk, vegetable oil, and vanilla extract, and mix until well combined. Stir in the boiling water until the batter is smooth.

Bake the Cake

Pour the batter into a greased 9x13 inch baking pan. Bake for 30-35 minutes or until a toothpick inserted into the center comes out clean. Let it cool completely before cutting into squares.

Chocolate Gelato

Heat the Base

In a saucepan, combine the milk, heavy cream, sugar, and cocoa powder. Heat over medium heat until the sugar and cocoa powder are dissolved, and the mixture is hot but not boiling.

Whisk in Egg Yolks

In a bowl, whisk the egg yolks. Gradually pour the hot milk mixture into the egg yolks while whisking constantly. Return the mixture to the saucepan and cook over low heat until it thickens slightly.

Chill and Churn

Remove from heat and stir in the vanilla extract. Let it cool, then refrigerate until cold. Churn in an ice cream maker according to manufacturer instructions until it reaches a soft-serve consistency.

Chocolate-Hazelnut Ganache

Make the Ganache

In a saucepan, heat the heavy cream until it just begins to simmer. Remove from heat and add the chopped dark chocolate and hazelnut spread. Stir until smooth and glossy.

Cookie Crumble

Prepare the Crumble

In a mixing bowl, cream together the butter and brown sugar until light and fluffy. Gradually add the flour and mix until crumbly. Fold in the chocolate chips.

Bake the Crumble

Spread the mixture on a baking sheet and bake at 350°F (175°C) for about 10-12 minutes or until golden brown. Allow to cool and crumble into pieces.

Whipped Cream

Whip the Cream

In a mixing bowl, combine heavy cream, powdered sugar, and vanilla extract. Whip until soft peaks form.