Start by heating your oven to 180°C (350°F). Grease two 8-inch cake tins with a little butter, then lightly dust them with flour. Place a circle of parchment paper in the bottom of each tin to prevent the cakes from sticking.

Add the blueberries, sugar, cornstarch, lemon juice, water, vanilla extract, and salt to a saucepan. Cook over medium heat, stirring often, until the blueberries soften and burst. Continue cooking until the mixture becomes thick and glossy. Set aside and let it cool completely.

In a large mixing bowl, beat the butter and caster sugar together until the mixture looks light and fluffy. Add the eggs one at a time, beating well after each addition. Stir in the vanilla extract until fully combined.

Gently fold the self-raising flour into the mixture. Pour in the milk and stir just until a smooth batter forms. Try not to overmix, as this helps keep the cake soft and tender.

Divide the batter evenly between the prepared cake tins and smooth the tops. Place them in the oven and bake for 25 to 30 minutes, or until a skewer inserted into the center comes out clean.

Leave the cakes in their tins for about 10 minutes after baking. Carefully remove them from the tins and transfer them to a wire rack. Allow them to cool completely before adding the filling and frosting.

Beat the butter until creamy and smooth. Gradually add the confectioners’ sugar, mixing well after each addition. Pour in the cream, vanilla extract, and salt, then continue beating until the frosting becomes light, fluffy, and easy to spread.

Cover the top and sides of the cake with the remaining frosting. Smooth the surface with an offset spatula. Chill for 20 minutes before slicing and serving.