I have made flakey crusts using butter, lard, and shortening (lie Crisco brand) and even cooking oil. The key to flakey pastry is to create the pea-sized granules of flour/salt/fat, don't overwork the dough (I use a pastry cutter to blend the ingredients together), and keep the dough cold, to maintain a certain amount of stiffness in the little dough balls if you will. When the dough warms, it tends to blend into a more homegenized mixture. The individual little dough balls, when chilled and mixed with a tablespoon or two of ice-water, turn into little flat-flakeswhen rolled out, weakly glued together by the wet starch. This allows the crust to be handled and formed to the pie-pan. When cooked, the moisture is mostly evaporated out, leaving a solid crust of flatened dough flakes, easily fractured when acted upon by pressure (provided by your teeth, a fork, knife, etc.).
Shortbread, on the other hand, is supposed to a continuous piece of pastry, with a fine and tender crumb. Both are great. Each has properties that make it more suited to one recpe type than the other.
If memory serves me correctly, use 1/3 cup of fat for every cup of flour (ratio = 3 to 1 of flour to fat respectively). Add about 2 tbs. ice water per cup of flour, after the fat, flour, and salt have been blended.
Seeeeeya; Goodweed of the North