Preheat the oven to 180°C (160°C for fan assisted ovens)/Gas Mark 4. Lightly grease 2 x 20cm round sandwich tins and line the bases with baking paper.
In a mixing bowl, stir the cake mix, oil, 180ml water and eggs gently together, then whisk (by hand or electric mixer) for 2-3 minutes until smooth and creamy. Divide the mixture equally between the 2 cake tins and level the tops. Bake for 23-28 minutes or until a round bladed knife inserted fully into the centre of the cakes comes out clean. Cool a little before turning out onto a wire rack to cool completely. Remove the baking paper.
To make the lemon strands for the decoration, pare the zest from the lemons in strips using a vegetable peeler, then cut into fine shreds with a sharp knife. Place in a saucepan with 200ml water and bring to the boil. Boil for 8 minutes, then stir in the caster sugar and let the mixture bubble over a medium heat for 10-12 minutes, without stirring, until nearly all the syrup has evaporated and the lemon strands are translucent (the syrup can burn quickly so reduce the heat after 5-6 minutes, if necessary). Use a fork to transfer the lemon strands to a plate lined with baking paper. Leave for about 30 minutes until cold.
Meanwhile, place 1 sponge on a serving plate or cake stand and, using a small palette knife, spread 1/2 tub of icing over the top. Spread over the lemon curd and top with the second sponge, pressing down gently. Spread 1/4 tub of icing in a thin layer over the top and sides of the cake to seal in the crumbs. Chill for 30 minutes.
Place the remaining 3/4 tub of icing in a bowl and beat in the cream until the icing has softened and has a glossy finish. Spread over the sides and top of the cake, creating large swirls with the tip of a palette knife. Chill for at least 30 minutes to allow the icing to firm up. Decorate the cake with the lemon strands to serve.
- Keep the cake in the fridge until ready to serve. Store the lemon strands in an airtight container in a cool place for up to 1 day. Use to decorate the cake just before serving.
- Adding cream to the icing gives it a lovely soft texture perfect for creating large swirls. Add the cream gradually and don’t over beat. If it seems a little too soft, just pop in the fridge for 30 minutes.