Heat the oven to 180C/350F/Gas Mark 4.
Beat the butter or spread with the sugar in an electric mixer for 3-5 minutes or until it is light and fluffy. Grate the rind from the lemon. One at a time lightly beat in the eggs with a tablespoon of flour then fold in the rest of the flour along with the lemon rind, the poppy seeds and the juice of ½ a lemon. Line an 18cm/7inch loaf tin with oiled nonstick baking paper. Spoon the mixture into the tin and tap the cake tin gently a few times on the counter top to flatten out the top.
Bake for 45 minutes or until a skewer comes out clean. Remove from the oven, allow to cool for a few minutes and then remove from the tin onto a rack and allow to cool completely. When the cake is cold, put the icing sugar in a small bowl and stir in up to 5 tsp of lemon juice - you want the icing to be quite thick but spreadable. Spoon it onto the top of the cake and then smooth it out with a spatula dipped in hot water, allowing the drips to run down the side of the cake.
Leave icing to set before cutting.
Freezing and defrosting guidelines
Bake according to the recipe but stop before adding decoration or icing. Allow to cool completely. Wrap well in clingfilm and tin foil (to prevent freezer burn) and freeze for up to 3 months.
Loosen the tin foil and clingfilm but leave to defrost in packaging at room temperature for several hours before serving.
If you wish to add icing or decoration, add them after the baked goods have fully defrosted and are at room temperature.
See more Gluten-free recipes