Does anyone know how to make the congee like those in Dim Sum/Yum Cha restaurants?
Congee itself is just thick rice porridge. It is usually made with a combination of short-grain and 'sticky' (glutinous) rice, but any kind of white rice will work.
Put 3/4 cup rice (1/2 cup regular, 1/4 cup sticky, if you have it) in a pot with 8 cups of water and a little salt. Bring to a boil and simmer for 1 to 1 1/2 hours, until it is a thick porridge. Stir now and then so it doesn't stick. Many electric rice cookers have a congee setting, which makes everything really easy - just put in a measure of rice, add water up to the congee mark, turn it on and wait.
There are many, many traditional toppings or additions to congee. Eileen Yin-Fei Lo said it well in her "From the Earth: Chinese Vegetarian Cooking": "Virtually any food can be added to one's breakfast congee in China. What you might add to it depends upon your preferences."