Preheat oven to 425 degrees. In a large bowl, mix together both flours and salt. Stir in tahini, oil, and 4 tablespoons of water. Knead in bowl until ball forms, add up to 1 tablespoon more water, if needed. Transfer dough to a lightly floured surface. You can also place the dough between two pieces of parchment paper and roll it out that way. Roll dough into a 12-inch round and fit it into a 9 1/2-inch tart pan with a removable bottom. Trim the extra dough. Then, pierce the bottom of the dough all over with a fork. Bake, rotating pan halfway through, until crust is golden brown and crisp, about 35 minutes. Let cool.