Put half the sugar and 1/2 cup water in a saucepan and bring to a boil; then simmer until the syrup thickens and turns golden brown.
Pour caramel into 4 ramekins (baking dish) so that the bottoms are evenly covered.
Preheat oven to 300°F or 150°C. Beat together eggs, egg yolks and remaining sugar.
Bring milk to a boil in a saucepan, then take it off the heat to cool a little.
Stir milk, orange juice and orange zest into the egg mixture and pour into the ramekins.
Place in a roasting pan, and fill pan with hot water so it comes halfway up the sides of the ramekins.
Bake custards for about 45 minutes. Check that water does not evaporate; top up as necessary.
Remove the custards from the roasting pan and leave to cool completely; put in the refrigerator.
Before serving, dip the base of each ramekin in hot water, and carefully loosen the sides of the custard with a sharp knife. Turn out onto dessert plates and serve.