Preheat the oven to 175°C (350°F). Grease and lightly flour a loaf pan or line it with baking paper, then set it aside.

Place the butter, caster sugar, and vanilla sugar into a bowl. Beat them together until the mixture becomes pale and creamy.

Add the eggs one at a time, mixing after each addition until the batter is smooth and uniformly combined.

Gradually sift or fold in the self-rising flour along with the pinch of salt. Stir just until the batter is even and free of lumps—avoid overmixing.

Transfer the batter into the prepared loaf pan and level the top. Bake in the preheated oven for about 60 minutes, or until set.

Near the end of baking, insert a wooden skewer or cake tester into the center; if it comes out clean, the cake is done.

Allow the cake to cool in the pan for a few minutes, then invert it onto a wire rack and leave it to cool completely before slicing.