Preheat oven to 180°C (350°F) and line three 8-inch cake tins with parchment paper.

In a stand mixer, cream 450g butter and caster sugar until light and aerated, approximately 5 minutes.

Incorporate eggs one at a time, ensuring each is fully emulsified before adding the next.

Gently fold in the self-raising flour, baking powder, and lemon zest using a large metal spoon to maintain volume.

Distribute the batter evenly among the prepared tins and bake for 35 to 40 minutes until the internal temperature reaches 98°C (208°F).

While the cakes are still warm, prick the surfaces with a skewer and liberally brush with elderflower syrup.

Allow the sponges to cool completely on a wire rack before leveling the tops with a serrated knife.

Prepare the buttercream by whisking 500g butter, powdered sugar, elderflower cordial, and milk until stiff peaks form.

Place the first layer on a cake board, apply a border of buttercream, fill the center with lemon curd, and top with the next layer.

Repeat the process for the second layer and top with the final sponge.

Apply a thin crumb coat of buttercream to the exterior and refrigerate for 30 minutes.

Apply the final layer of buttercream using an offset spatula for a smooth finish and garnish with fresh edible flowers.