Preheat the oven to 175°C. Grease four 5-ounce ramekins and sprinkle them with sugar, tapping out any excess. Place these in a larger pan (such as a roasting pan).
Sprinkle the berries evenly on the bottom of each dish.
Stir the sugar, flour, lemon zest and salt to combine. Add the lemon juice, milk and egg yolks to this and whisk until smooth.
Whip the 2 egg whites until they hold a soft peak when the beaters are lifted. Fold this into the batter until fully incorporated and divide this between the ramekins. Pour boiling water around the baking dish and bake for about 35 minutes, until golden brown on top. Allow the cake to cool for 15 minutes in the water bath, then remove the ramekins from the water and either continue cooling on a rack or invert onto a plate, revealing the berries and warm lemon curd sauce. Serve warm or at room temperature.