Begin by preheating your oven to 160°C (320°F) in static mode. Lightly grease a 20cm (8-inch) round cake tin and line it with parchment paper. If you're using a non-stick tin, you can skip greasing and lining. Sift the plain flour and baking powder into a mixing bowl. Add the caster sugar and a pinch of salt, then stir everything together with a spoon until evenly combined. For the best texture, opt for extra-fine sponge cake flour if available. If you prefer a sugar-free option, substitute the caster sugar with granulated erythritol, a natural zero-calorie sweetener.

In a separate bowl or measuring jug, dissolve the butterfly pea powder in a small amount of the plant-based milk, stirring thoroughly until there are no lumps. If you don’t have the powder, you can use dried butterfly pea flowers—just follow a butterfly pea latte recipe, then cool the blue milk completely before using it in the cake. Next, separate the egg yolks from the whites, placing the yolks in the butterfly pea milk mixture and the whites in another bowl to be whipped later. Beat the yolks into the colored milk until smooth and creamy. Then add the remaining plant-based milk and the melted, cooled coconut oil to the mixture, stirring to combine.

Pour the blue milk mixture into the dry ingredients. Use an electric whisk to blend everything together until you have a smooth, creamy batter with an even blue color. Once the batter is ready, set it aside and prepare to whip the egg whites.

With a clean electric mixer, beat the egg whites until they become fluffy and form stiff peaks. It’s best to start at a low speed and gradually increase as the egg whites begin to foam. Once they reach stiff peak consistency, fold them gently into the cake batter a few spoonfuls at a time. Use a spatula to incorporate them, folding from top to bottom to maintain the airiness of the batter.

Pour the prepared butterfly pea cake batter into the cake tin, spreading it out evenly. Place the tin on the bottom rack of your oven and bake for 50 to 60 minutes. The cake is done when a skewer inserted into the center comes out clean, with no wet batter or crumbs sticking to it.

After baking, remove the cake from the oven and let it sit for a few minutes to cool slightly. Carefully remove it from the tin and place it on a wire rack to cool completely before slicing. Once cooled, dust the top with icing sugar if desired. Your butterfly pea cake is now ready to enjoy!