Preheat the oven to 160°C
Grease a baking dish with butter
Cream together the butter and sugar, then add the lemon zest and optional marmalade and mix until combined
Slowly add the egg yolks one at a time, beating well between each addition
Slowly add the flour and milk and when combined, slowly add the lemon juice to complete the batter
In a very clean, dry bowl, whisk the egg whites until peaks form
Add one-third of the whites to the lemon mixture and gently fold in. Then gently fold in the remaining egg whites
Pour the mixture into the prepared dish/es and place in a deep-sided water bath
Cook for 40 minutes, or until risen and golden on top
Remove from the oven and dust with a flourish of icing sugar
Serve warm with cream. Alternately, cool and put into the fridge to serve chilled
