You just need pantry staples ot make this: eggs, butter, flour, sugar, milk and lemon.
Whisk the egg whites until they forms stiff peaks. This is the part that helps to add some lightness to the dessert's topping.
Use a separate bowl to first cream the sugar and butter, then add in the rest.
You are looking to get a balance between being mixed but not losing too much air in the egg white. A few lumps here and there is fine.
By placing the dish with the pudding cake mixture inside another dish with water, it helps keep the cooking temperature more even.
This dessert has a lovely mix of tanginess and sweetness. And so easy, too. Enjoy!