Add the lemon zest and one egg at a time beating well between each egg until smooth.
Sift flour and gently fold into the mixture.
Add washed and dried blueberries and mix in gently.
Place the cake mix in the muffin tin lined with cupcake cases. Bake for about 25-30 minutes (until golden) in a preheated oven at 190 C, 180 °C fan, Gas mark 5. Allow to cool after baking.
Prepare the icing: mix Stork with the sugar. Place the half of the icing in a piping bag. Then mix the blueberry jam with the remaining icing in a bowl and after stirring a bit also place it in a piping bag.
Cover the muffins with the icing using a piping bag fitted with a star nozzle or just spread over and decorate with the fresh fruit.