Preheat the oven to 180 C / Gas 4 and line a couple of cupcake trays with 18 paper cases.
For the cupcake mixture cream caster sugar and butter together until a light and fluffy consistency has been achieved.
Sieve in the self-raising flour, cornflour and baking powder and stir. The light and fluffiness should now have transitioned into a sort of gritty consistency.
Next whip together the eggs, orange zest and Pimm's. Add to the cake mixture and stir until smooth as much as your arms can muster.
Crush the raspberries and the strawberries (making sure you save some for the topping – see my photos, I plonked a strawberry on every cake but obviously you can use half…whatever takes your fancy!) and fold them into the cake mixture.
Place the mixture into the cases and bake in the preheated oven until a toothpick comes out clean, 20 to 25 minutes.
For the syrup put the sugar and the Pimm's in a saucepan and bring to the boil at medium-high heat until the sugar has dissolved. Increase the temperature and let it boil till syrupy, about 5 minutes. Pour into a jug and let it cool.
After the cakes have baked, place on a cooling rack and prick the tops of the cakes with a toothpick and brush them with the Pimm's syrup.
Whilst they are cooling, make the buttercream by blitzing the icing sugar, Pimm's and butter together with an electric mixer. Add more or less icing sugar to get the perfect consistency – it should be pipable. Pop in the freezer for 20 minutes if it seems too warm.