Preheat the oven to 180°C fan. Grease and line a loaf tin measuring approx 11 x 21cm, set aside.
Place butter, sugar, lemon zest, 1 tablespoon of lemon juice and vanilla or almond extract in the bowl of a free-standing food mixer with the paddle attachment in place. Beat for a few minutes, until light and pale. Add the eggs, one by one, scraping down the sides of the bowl. The mix may split a little, but it'll come together once you add the flours. Add the gluten free flour, salt and almond meal and pour into the prepared loaf tin.
Bake for 45 to 55 minutes or until springy to the touch, test by inserting a knife into the middle: it’s ready if it comes out clean. Remove from the oven and set aside to cool for 10 minutes, then remove from the tin and place on a wire rack to cool completely.
To make the icing. Put 1 or 2 tablespoons of lemon juice into a bowl with the icing sugar and whisk until smooth. You might need more lemon juice to get the right consistency but add it slowly. Pour over the cake and gently spread out.
