Complex sentence: Shortbread is different from shortcake, which can be similar to shortbread, but which can be made using vegetable fat instead of butter and always uses a chemical leavening agent such as baking powder, which gives it a different texture.
Split into simpler sentences: Shortbread is different from shortcake, which can be similar to shortbread. The difference is that shortbread can be made using vegetable fat instead of butter and always uses a chemical leavening agent such as baking powder, which gives it a different texture.