Set your oven to 350°F/180°C/160°C Fan/Gas mark 4.
Insert a loaf tin liner or line the base of your loaf tin with greaseproof paper and grease the exposed ends of the tin with some extra butter
Sift together your flour, baking powder and salt.
Rub your lemon zest into your caster (superfine) sugar.
Using the paddle attachment for your stand mixer or beaters for your hand mixer, beat your butter a few times to ensure nice and soft. It should no longer be clumping around the paddle/beaters when soft enough.
Add your caster sugar and rubbed in lemon zest and beat until a dry paste is formed, this takes about a minute.
Mix together your yoghurt and lemon juice and then add it all to your beaten butter and sugar, beat together a few times until just combined and wipe your bowl down with your spatula intermittently to ensure everything is equally mixed.
Add an egg and a tablespoon of your sifted flour mixture and beat on a low setting until combined and no unmixed egg remains.
Repeat until the eggs are all mixed in.
Lightly beat in the remaining flour until just combined, again wiping down with your spatula to ensure all of the batter is mixed in.
Give the mixture a fast beat on medium-high for 10 seconds and no more. It should be mixed and look silky when ready.
Pour the mixture into your prepared tin and level out.
Place in the centre of your oven and bake for 35-40 minutes, until golden on top and skewer inserted into the centre comes out clean.