Line a loaf tin with baking parchment. Tip the butter, sugar, eggs, flour, a pinch of salt and two-thirds of the lemon zest into a bowl, then beat with an electric whisk for 4-5 mins until pale and fluffy.

Heat the air-fryer to 160C. Spoon the cake mixture into the prepared tin, smoothing the surface. Cook for 1 hr-1 hr 10 mins until a skewer inserted in the centre comes out clean (you can cover the surface with foil if it starts to get too dark). Leave to cool in the tin for 5 mins.

Meanwhile, combine the icing sugar, remaining lemon zest and just enough juice to make a smooth, pourable icing. Carefully lift the warm cake out onto a wire rack set over a tray and poke deep holes all over the top using a skewer. Slowly drizzle over the icing, letting it drip off the edges. Leave to set before serving.