This delightful, zesty and citrusy whoopie pie, with a light and fragrant honey buttercream filling, can be made a few days in advance to allow all the flavours to completely infuse.
Preheat the oven to 180°C/350°F/Gas 4. Line two baking trays with baking parchment. Whisk the butter, sugar and vanilla seeds in a bowl until fluffy. Whisk in the egg.
In a separate bowl, sift the flour, bicarbonate of soda and salt. Add the orange rin