Preheat the oven to 350°F (180°C). Grease a 12-cavity mini loaf pan or one 1-pound loaf pan.
Beat the softened butter and caster sugar until light. Beat in the egg yolks, then mix in the yogurt and lemon zest until smooth.
Fold in the self-raising flour just until combined.
In a separate bowl, whisk the egg whites to soft peaks and gently fold into the batter.
Divide the batter between the mini loaf cavities. Bake 25–30 minutes, or until golden and a skewer comes out clean (a single loaf may take 40–45 minutes).
Cool in the pan for 10 minutes, then turn out onto a rack to cool completely.
For the glaze, mix the powdered sugar with lemon juice until smooth. Spoon over the cooled loaves and top with crushed pistachios.