Melt the butter – Heat the 120 g water until nearly boiling, then pour it into a bowl or glass measuring cup. Add the cubed 113 g butter and stir until melted.
Mix dry ingredients – In a large bowl, combine the 310 g all purpose flour and 9 g fine sea salt.
Combine wet and dry – Pour in the hot water-butter mixture and add the 270 g sourdough discard. Mix by hand or with a dough whisk until a sticky dough forms.
Knead – Knead by hand for about 10 minutes until the dough becomes smooth and elastic.
Rest – Cover and let the dough rest for 30 minutes.
Divide and shape – Form the dough into 12 equal balls. Adjust the size depending on how big you want your tortillas. Cover and rest for another 30 minutes.
Preheat your skillet – Heat a dry skillet (cast iron, carbon steel, or a comal) over high heat.
Roll out the tortillas – Lightly flour a surface, your rolling pin, and the dough. Roll out each ball as thin as possible, rotating for an even shape.
Cook – Place a tortilla in the hot skillet. Small bubbles should form within 10–30 seconds. Flip and press down gently with a spatula to deflate large air pockets. Cook until golden brown spots appear.
Steam & soften – Stack the cooked tortillas and wrap them in a clean kitchen towel to keep them warm and soft.