Whisk the flour and salt together in a large mixing bowl.
Combine the milk and butter in a small saucepan over low heat. Stir occasionally until the butter melts, then remove from the heat.
Pour the warm milk mixture into the dry ingredients and stir until a shaggy dough forms.
Transfer to a lightly floured work surface and knead for about 2 minutes, until smooth and pliable.
Cover and let rest for 30 minutes.
Divide the dough into 6 equal portions. Shape each into a disk and roll into an 8-inch circle.
Heat a dry cast iron or nonstick skillet over medium-high heat. Cook each flatbread for 1 to 1½ minutes per side, until golden-brown spots develop, and the dough is cooked through.
Stack the cooked flatbreads on a plate and cover with a clean kitchen towel to keep them soft and flexible until ready to serve.
Notes
If the flatbread browns too quickly, reduce the heat slightly. If it remains pale and doesn't puff, increase the heat.
Use only enough flour to prevent sticking when kneading and rolling. Excess flour can make the finished flatbread dry.
Prepare the dough up to 24 hours in advance and refrigerate it covered. Allow it to lose its chill before rolling and cooking.
Store cooled flatbreads in an airtight container at room temperature for up to 2 days or refrigerate for up to 5 days.
Freeze cooked, cooled flatbreads in a freezer-safe container or bag for up to 2 months. Reheat directly from frozen in a dry skillet.