Heat the oven to 400°F. In a large bowl, combine the flours and salt, and whisk to combine. Using the large holes of a grater, grate the cold vegan margarine into the flour mixture, tossing to coat the shreds with flour. Work the margarine in just a little by squeezing the mixture with your fingers to break the shreds into smaller pieces, about the size of peas. Sprinkle in about 3 tablespoons of ice water, fluffing the mixture with a fork. Add water a tablespoon at a time, and start to gently turn and squeeze the dough as it forms. Once all the flour is moistened and the dough starts to hold together in a ball, flatten the dough ball to form a disk.