In a medium saucepan, melt 80g of unsalted butter over low heat, then stir in 100ml of milk, 100ml of water, and ½ teaspoon of salt until fully melted and combined.

In a mixing bowl, whisk together 150g of all-purpose flour and 1 teaspoon of baking powder. Gradually pour the flour mixture into the boiling liquid, stirring constantly until it forms a smooth dough.

Allow the dough to cool slightly for about 5 minutes before incorporating the eggs one at a time.

Preheat your oven to 400°F (200°C) and line a 25cm round cake pan with parchment paper. Divide the prepared dough into two equal portions and spread each evenly in the pan.

Bake in the preheated oven for about 20 minutes until golden brown and springy.

While the layers cool, beat 4 eggs with 100g of sugar in a mixing bowl until pale and thick. Gradually mix in 50g of flour, followed by 100ml of milk.

Transfer the mixture to a saucepan, then cook over medium heat while stirring until it thickens.

In a separate bowl, beat 180g of softened unsalted butter until light and fluffy, then blend in the cooled cream mixture.

Layer the cooled cake on a serving platter, spread half of the cream on top, place the second layer, and finish with the remaining cream.

Refrigerate for at least 2 hours, dust with icing sugar, slice, and serve.