Place flower and alt in a bowl. Grate the butter on the coarse side of a box grater, then cut it into the dry ingredients with two knives, a pastry cutter, or your fingertips. Add the lemon joice and mix, tossing with your fingers or with a fork. Add cold water, 2 tablespoons at a time, until the pastry just comes together: you will need from 4 to 6 tablespoons of water, depending on your flour. Pull the dough together and place in a heavy plastic bag. Flatten (from outside the bag) into a disk. Then remove from the bag and cut in two. Put each piece in a heavy plastic bag, and flatten into a disk. Seal well and refrigerate for at least 30 minutes, or up to 2 days, or freeze for up to a month