What is trex? How can I use it? Can I buy it in an on-line shop? Thank you.
Trex is a solid vegetable fat brand sold in the UK, it is available in most major supermarkets. You can also use Flora White as an alternative, or lard if you don't mind animal fats. It is mainly used as an ingredient for pastry - using lard or vegetable shortening gives a crisper, flakier pastry and generally in pastry a combination of butter and shortening (usually in the ratio of half the total weight of fats to flour) gives the best results. Vegetable shortening can also be used for frying. It has a high "smoke point" (meaning it can be hated to higher temperatures without burning, unlike butter or olive oil) so can be good for searing or for deep fat frying and it is also a useful fat to use if making Yorkshire puddings (popovers) as they are baked at a high temperature.
In the US Crisco is the most common brand of vegetable shortening but there are also others available, such as Earth's Balance. Most brands of vegetable shortening should be good substitutes for Trex in recipes.