1) Place the flours, salt and xanthan gum in the bowl of your mixer and stir to combine.
2) Add the water, oil and egg and blend well, turning the mixer to medium-high speed for about 1 minute. The dough should be very thick.
3) Allow the dough to rest for about 15 minutes. While it's resting, prepare several sheets of half-sheet parchment paper by cutting them in half and spraying one side of each piece with oil.
4) Preheat your stove-top or electric griddle to medium heat. Scoop a 2-tablespoon ball of dough onto a piece of the parchment; a jumbo cookie scoop works well here. Cover with another piece of parchment, making sure that the oiled sides are touching the dough. Using a rolling pin or pastry roller, roll the dough into a 6 1/2" circle.
5) When the griddle is hot, peel back the paper on one side of a tortilla and flip it, paper-side up, onto the griddle. After 10 to 15 seconds, peel off the second piece of paper by pulling it directly backward and away from you; it should peel away cleanly. Flip the tortilla immediately and cook for another 10 to 15 seconds.
6) Repeat with the remaining tortillas, placing as many on the griddle as will fit.
7) Serve warm or cool before wrapping and storing.
Yield: 18 medium (6") tortillas.