The basis of shortcrust pastry is 'half fat-to-flour', of which butter is the most common fat used, with a small amount of ice cold water added at the end to bring the pastry together. Many recipes use a 50:50 split of butter and lard, as lard improves the texture of the pastry, though the flavour won't be quite as rich and buttery. Another option is to use vegetable shortening, which means that the pastry is also suitable for vegetarian and vegan diets.
Pastry-making is a pastime which favours those with cold hands - cooks often work on a marble slab to help keep the pastry cool. It is important to keep cool, because if the butter is heated too much it becomes oily, which smothers the flour so the grains aren't able to absorb the water properly. If the flour can't properly absorb water, it will be too crumbly and be hard to roll.