Collect equipment and ingredients. Place butter in a microwave safe bowl and microwave to just melt. Set butter aside to slightly cool.
Place a large bowl on your food scale and tar to set. Measure 150 g of sourdough discard. This can be active or inactive starter; mine is usually leftover discard straight from the refrigerator. Using your spatula, combine melted butter with starter and mix well. Add in remaining ingredients: 200 g flour, 10 g salt and 70 g water. Mix with spatula until just combined.
Dump dough onto flat floured surface to knead. Knead dough by forming into a ball, press ball firmly with palm of hand, then roll back into a ball. Repeat this process for 3-5 minutes. Form dough into a ball, cover with plastic wrap or a damp towel and let rest for at least 30 minutes.
Using a bench scraper, divide dough ball in half. Working with one half of the dough, cut in half, then half again. Repeat process with remaining half of dough so that you have eight to ten equal size portions (depending on final desired size of tortilla. Dividing into 8 will yield approximately 8 inch round tortillas). Roll each portion into a ball and cover or place into a container to rest. Rest again for another 10 minutes, or place in fridge to rest for up to 24 hours.
Remove dough from fridge and let set on counter for 30 minutes to remove the chill. Set up surface with a small bit of flour and rolling pin. Sprinkle dough very lightly with flour to prevent sticking, then roll out each dough ball into a thin disk approximately 6-8 inches in diameter. Dough should be approximately 1/8th inch thick.
Preheat iron skillet to medium high heat. Skillet should be hot and smoking when ready. Place tortilla in skillet and cook for 1-2 minutes until just starting to brown. Flip with a spatula and repeat on the second side for another minute until just starting to brown.
Serve warm with your favorite toppings or accompaniments. Or just enjoy plain!