Heat oven to 160C/fan140C/gas 3. Prepare the inside and outside of a 23cm tin, as before. Cream the butter and sugar together until light and fluffy, then gradually beat in the eggs a little at a time. Add a tbsp of the plain flour if it starts to split. Fold in the flours and a pinch of salt, followed by the lemon zest and juice.
Spoon the mix into the tin and bake for 1 hr 35 mins or until well-risen and golden and a skewer inserted comes out clean. Meanwhile, make the syrup by heating the sugar, lemon zest and juice in a small pan until the sugar dissolves. Set aside.
Once the cake is out of the oven, leave to cool until it’s just warm, then use a skewer to poke holes down to the bottom all over the cake. Pour the syrup over, letting it completely soak in after each addition. Leave to cool completely, then either wrap or fill and ice the cake. The unfilled cake will keep well if you wrap it with baking parchment and cling film for up to 4 days, or in the freezer for up to a month.