Preheat your oven to 170°C (340°F). Grease your cake tin and line the base with parchment paper to prevent sticking.

In a clean, dry mixing bowl, beat the egg whites until they become foamy. Gradually add 50 g of caster sugar and continue whisking until stiff peaks form. Set aside.

In a separate bowl, cream the softened butter with the remaining 100 g of caster sugar until the mixture is light and fluffy. This should take about 3–5 minutes with an electric mixer.

Add the egg yolks one at a time, mixing well after each addition. Stir in the orange juice, orange zest, and orange extract (if using), blending until fully combined.

Sift together the self-raising flour and baking powder. Gradually fold the sifted dry ingredients into the butter mixture until just incorporated. Avoid over mixing to keep the batter light.

Gently fold the beaten egg whites into the batter in 2–3 additions to preserve the volume and lightness. Pour the finished batter into your prepared tin and smooth the top.

Bake for 45–50 minutes, or until a skewer inserted into the center of the cake comes out clean. Allow the cake to cool in the tin for 10 minutes before transferring to a wire rack to cool completely.