1) Preheat oven to 170°C/Gas 3. Butter and lightly sugar four ramekins, each about the size of a cup.
2) In a mixer, add the egg yolks, buttermilk, lemon juice and lemon zest and beat until well combined. Reduce the speed to low and sift in the flour, sugar and salt. Continue to mix until combined.
3) Beat the egg whites until you get stiff peaks then combine the two mixtures by gently folding them together, a little at a time. Divide evenly among the ramekins then bake in a water bath; set the ramekins in a roasting tray and fill with water to halfway up the sides of the dishes.
4) Bake for 60 minutes, until the tops spring back when gently pressed and the cakes have a nice golden brown color. Allow to cool slightly, then carefully invert them onto a plate.
5) Serve with fresh berries and dust with icing sugar.