Preheat your oven to 175°C (350°F). Grease a 9x5 inch loaf pan with butter and lightly dust with flour or line with parchment paper.
Split the vanilla beans lengthwise and scrape out the tiny seeds into a small bowl. Set aside.
In a large mixing bowl, beat the softened butter and superfine sugar together with an electric mixer or whisk until the mixture is pale, fluffy, and fragrant, about 3-4 minutes.
Add the vanilla seeds to the butter mixture and mix until evenly distributed, releasing a rich vanilla aroma.
One at a time, beat in the eggs, ensuring each is fully incorporated before adding the next. The batter will become smoother and slightly thicker.
In a separate bowl, whisk together the flour, salt, and baking powder.
Gradually add the dry ingredients to the wet mixture, folding gently with a spatula after each addition to keep the batter light and airy; stop mixing once just combined.
If the batter feels very thick, fold in 2-3 tablespoons of milk or cream to loosen it up slightly.
Pour the batter into the prepared loaf pan, smoothing the top with a spatula. Gently tap the pan on the counter to settle the batter and remove air bubbles.
Bake in the preheated oven for 50-60 minutes, until the cake is golden, fragrant, and a toothpick inserted into the center comes out clean. If the top browns too quickly, tent with foil after about 45 minutes.
Remove the cake from the oven and allow it to cool in the pan for 15 minutes. Then, transfer to a wire rack to cool completely before slicing to reveal a tender, aromatic crumb.