Pre heat your oven to 160C Fan/180C/350F/Gas Mark 4 and line a muffin tin with cupcake cases
Mix together the butter, sugar and lemon zest until light and fluffy, ideally using an electric mixer
Add the eggs and whisk in
Add the self raising flour and whisk in gently
Divide the mixture between the cupcakes cases, then add 4 blueberries to each cupcake and press them into the batter
Bake them for 20-25 minutes or until a skewer inserted comes out clean (it may have some bluberries juice on it but that's ok.) Put them on a rack to cool completely
To make the buttercream mix together the icing sugar and butter using an electric hand whisk or food mixer until they start to come together, then add the lemon extract and milk, and mix until smooth. You can also add some extra milk if the buttercream is too stiff
Put the buttercream into a piping bag fitted with a nozzle of your choice and pipe it onto the cupcakes
Add blueberries and lemon zest to decorate
Store in an airtight container in a cool place, eat leftovers within 3 days