Preheat your oven to 180°C (160°C for fan assisted ovens) / Gas Mark 4. Line a muffin tin with your cupcake cases.
Mix the eggs, oil, water, Vanilla Cupcake Mix, and the lemon zest gently together and whisk (by hand or electric mixer) for 2-3 minutes until smooth and creamy.
Pour the mixture evenly into the cupcake cases.
Bake in the centre of the oven for 16 minutes or until a rounded knife, inserted fully into the centre of a cupcake comes out clean, then cool on a wire rack.
Loosen the lemon curd with 2 tsp of the lemon juice. Hollow out a little of the centre of the sponge and fill with 1 tsp of lemon curd. Repeat with all the cupcakes.
Whisk together the icing with the butter and remaining lemon juice, until smooth. Spoon into a piping bag fitted with a star nozzle. Squeeze onto the top of the cupcakes.
Drizzle the remaining lemon curd over the cupcakes. Decorate with the edible flowers.