In a medium bowl, whisk together the flour and salt.
Cut the butter into small chunks and add to the flour mixture. Press the butter into the flour with your hands until you have small pea sized crumbs.
Stir in the water and sourdough starter and mix until the dough comes together in a ball. The dough should be soft but not sticky.
Turn the dough out on to a clean surface and knead for 2-3 minutes, or until the dough is smooth and supple.
Place the dough back in the bowl, cover, and let rest at room temperature for 2 hours. You can also let the dough rest in the fridge overnight.
Divide the dough into 12 equal pieces (about 44 grams each) and then shape into small balls.
Use a tortilla press to press each tortilla dough ball as thinly as possible. If you're having trouble with tortillas sticking, you can place the dough ball between two pieces of parchment paper.
Heat a large cast iron skillet over medium high heat.
Place a pressed tortilla in the skillet and cook until it puffs up and begins to brown (about 30 seconds). Then flip and cook on the other side for 30 more seconds. Repeat with each tortilla.
Notes
Store cooked tortillas in an airtight container at room temperature for up to 5 days or in the freezer for up to 2 months. You can store the uncooked dough in the fridge for up to 2 days.