It's not easy to get excited about oranges. The fruit is a victim of its own popularity - it is ubiquitous throughout the year, even though its true season is the winter. It's only when we taste a particularly juicy, sweet and delicious one that we think twice about a fruit most of us take for granted.
Most types of orange we buy are seedless (this isn't true for Citrus reticulata, the loose-skinned variety which includes tangerines and mandarins). They're usually of the orange-skinned navel variety but there are many others - and they come in a range of colours. You may occasionally come across blood oranges, which have reddish flesh, and the green-skinned, orange-fleshed Thai variety (which makes the most delicious juice). I haven't seen Seville oranges - the tart, seedy, thick-skinned variety used to make bitter marmalade - in Hong Kong.
As with other types of citrus, look for oranges that feel heavy for their size - that means they'll be juicy. The zest - the coloured part of the skin - is fragrant and flavourful but avoid using the pith (the white part under the zest) because it's bitter.
Because oranges are so juicy, it's difficult to cook with them: the liquid the flesh exudes needs to be taken into consideration otherwise the dish will be watery. Fresh orange juice works well in custards, although if the fruit is too acidic, it can curdle the cream or milk. To avoid this, whisk the egg and sugar first, then thoroughly whisk in the juice before adding the cream or milk. If adding zest (and you should), whisk it in after the custard has been strained.
Fresh orange juice adds a sweet-sour note to the pork-braising liquid of the Mexican dish carnitas. Mix the juice with chicken broth, fresh lime juice, cola or honey (to give colour and sweetness), garlic, dried oregano and salt and pepper. Add the pork and slowly bring to a simmer before reducing the heat and cooking until the meat is very tender and the liquid has reduced to a thick syrup that coats the pork. Remove as much fat as possible from the liquid then increase the heat and cook to crisp up the pork. Roughly chop the meat and serve it in tortillas with salsa and guacamole.