Mix your dry ingredients. Mill your wheat berries fine, then stir in the salt and baking powder until well combined.
Cut in the fat. Add your tallow or lard to the flour mixture and cut it in until it resembles coarse sand. A pastry cutter works great here, but two knives or even your hands will get the job done.
Add your water gradually. Make a well in the center of the flour and add warm water a little at a time, mixing as you go. You're aiming for a dough that holds together, is workable, but isn't sticky. You may not need the full 1 1/2 cups, so add slowly and stop when the dough comes together.
First rest. Cover the dough and let it rest for 15 minutes. This gives the bran time to hydrate and soften, which makes a real difference with fresh milled flour.
Knead. After the rest, knead the dough for 5 to 10 minutes. I did this by hand, and it's a nice way to feel the dough change as the gluten develops.
Second rest. Cover and let the dough rest again for 15 to 20 minutes.
Divide and shape. Portion the dough into balls, smaller for taco size and larger for burrito size. Place the balls in a bowl and keep covered while your griddle heats.
Heat your griddle. Get it to medium heat before you start rolling.
Roll thin. Here's the part that surprised me most. Roll each dough ball in flour before you ever pick up the rolling pin. Once it's coated, roll it out as thin as you can get it. You want to almost see through it.
Cook. Place the tortilla on the hot griddle and cook 15 to 20 seconds per side, flipping every 15 to 20 seconds until it stops puffing.
Keep warm. Transfer finished tortillas to a towel lined bowl and keep covered so they stay soft while you finish the batch.