Preheat the oven to 350. Grease an 8x8 baking dish or 4 6oz oven-safe ramekins.
Set water on to boil.
In a medium bowl, combine the sugar, flour, and salt. Set aside.
In another bowl, combine the lemon juice, zest, butter, and milk.
Separate the eggs into 2 more bowls.
Beat the egg yolks until thick and pale. Set aside.
Wash the beaters really well and dry them then beat the egg whites until stiff but not dry. Set aside.
Stir the butter/lemon mixture into the dry ingredients then stir the whipped egg yolks into that.
Fold the beaten egg whites into the lemon mixture.
Pour the batter into the prepared baking dish or ramekins.
Place the filled dish into a larger pan then pour hot water about 1-inch deep in the larger pan to create a water bath.
Bake for 35-40 minutes or until the topping is set and golden (if you bake for too long, the pudding will dry up.)
Serve warm.