Preheat the oven to 325 degrees F.
in a bowl. Add the brown sugar
, and mix well.
Place the milk, cream and orange zest
, if using, into a saucepan
and bring up to a simmer
. Remove the saucepan from the heat, and gradually pour into the egg and sugar mixture, whisking continuously. Pour the custard
mixture through a sieve
and into a large jug, and skim
off any froth from the surface.
Place the cups or ramekins in a baking dish
, or wide shallow pan, and fill them up with the custard. Pour enough hot water into the baking dish to come halfway up the sides of the cups or ramekins (known as a bain-marie) and cover with foil. Bake in the oven for about 40 minutes, or until the custards are just set in the center.
Remove the custards from the baking dish, and serve warm or allow to cool. Either way, sprinkle a little bit of extra brown sugar on top just before serving.