In a large bowl, place the flour, xanthan gum, masa harina, salt, and baking powder, and whisk to combine well.

Add the shortening and cut in with a pastry blender, two knives, or your fingers (it doesn’t need to stay cold, so your hands work fine here) until evenly distributed throughout the dry ingredients.

Add the water to the mixture slowly, mixing constantly. The dough will begin to come together.

Depending on the climate in your kitchen, you may need more water than 1/2 cup, and you made need less. After 1/2 cup, add the water sparingly by the tablespoon, kneading well after each addition.

If the dough is crumbly, it is too dry and needs a bit more water. If it is sticky, it is too wet and could benefit from another teaspoon of masa. Add all ingredients sparingly.

Knead the dough for about 5 minutes, until smooth and well integrated, cover with a towel, and allow to rest on the counter for 30 minutes.

Once the dough has rested, divide it into 8 to 10 equal parts (depending upon how large you want your tacos), and roll each into a ball.

Roll between two either two sheets of plastic wrap or a gallon-sized Ziploc bag, split down the seams and then cut in half. Use a tortilla press (lined with plastic on both sides) if you have one – they’re worth the small investment.

Cook each round of dough in a heavy-bottom cast iron (or nonstick) skillet over medium-high heat for 20 seconds on one side (pressing the tortilla gently in the center with a wide spatula as it cooks), flip and cook for 10 seconds on the other side.

The tortilla should be completely opaque and lightly charred in spots.

Remove the tortilla from the pan, and place either in a tortilla warmer or in a moist tea towel, covered on both sides with the towel. Repeat with the remaining rounds of dough, and serve warm.