Preheat the oven to 325 degrees F.
the eggs 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.