Preheat the oven to 180°C/350F/Gas 4. Grease and line a 2lb loaf tin.
Add the lemon juice to the milk and leave to stand for 10 minutes until curdled and lumpy.
Sift the flour, baking powder and bicarbonate of soda together into a large bowl.
Add the caster sugar, lemon zest, chopped thyme and salt and stir to combine.
Add the oil and vanilla to the milk mixture and pour into the flour mixture. Fold in with a metal spoon until combined.
Spoon the mixture into your prepared tin, gently level the surface and bake for 30 – 40 minutes until golden brown. Test if it’s cooked by pushing a skewer into the centre, if it comes out clean it is ready.
Leave to cool for 10 minutes before turning out on to a wire rack to cool completely.
Once the cake is cool make the icing. Sift the icing sugar into a small bowl and add the lemon juice a little at a time until you have a spooning consistency. Stir in the chopped thyme.
Place the cake on a wire rack over a tray. Spoon the icing over the cake and allow to drip down the sides. Leave to set for about an hour - if you can wait that long!