Milk
Most people don't specify the type of milk they mean when they talk about the ingredient, but it's something produced by all species of mammals. Although few humans have had the opportunity to taste milk from whales (reportedly the richest and fattiest of all milks, but probably rather fishy tasting), seals or dolphins, many other types of mammals have been domesticated for their milk, such as cows, goats, camels, yaks and reindeer. The flavour of milk varies according to the animal it comes from and what they eat.
Milk is used to make a number of products and has many byproducts, such as butter, cream, cheese, buttermilk, whey, yoghurt, sour cream, cream cheese and canned and powdered milks. Although raw milk is believed to be more nutritious and flavourful (and makes the best cheeses), it is a good medium for harmful bacteria and micro-organisms. Farms making products from raw milk have to adhere to the strictest hygiene standards. Because raw milk is potentially dangerous, it is usually pasteurised (heated and quickly cooled), which extends its refrigerated shelf-life from a day or so to more than a week. When milk and cream are treated to ultra-high temperatures (UHT), they have a much longer shelf life and don't need to be refrigerated. Unfortunately, it also gives the liquid an odd, burnt taste. Although Hong Kong has dairies making fresh milk, almost the only cream available is imported UHT.
While milk products are a good source of calcium, many people - particularly those of Asian and African descent - are lactose intolerant, meaning they can't easily digest milk sugars. The severity of symptoms varies: some are able to tolerate ice cream and some cheeses because they contain small amounts of lactose, while others can't eat any milk products. One exception seems to be fresh yoghurt because it contains active cultures that break down milk sugars.
Macaroni and cheese is a simple, homey dish, the flavour of which can vary if different cheeses are used. Saute a chopped onion in 60 grams of unsalted butter. When the onion is soft, stir in a tablespoon of grainy mustard, salt and pepper and 40 grams of plain flour. Stir over a low heat until the flour loses its raw taste. Slowly add 600ml milk, stirring constantly so it doesn't form lumps. Add 250 grams of grated cheese (such as a sharp or mild cheddar, Emmantal, gouda or gruyere), a few drops of Tabasco and Worcestershire sauce, grated nutmeg and salt and pepper to taste. Mix the sauce with cooked macaroni and spread into a buttered baking dish. Sprinkle with bread crumbs mixed with grated Parmesan cheese and bake until hot and brown.