In a large bowl add the yeast (7g) and warm water (300g). Add a pinch of the sugar. If using active (not instant) yeast, let sit 10 minutes until frothy. If using instant yeast, continue.
Whisk in the sugar (10g), yogurt (170g), the salt (12g), and olive oil (25g).
Add ~450 grams of the flour and (if using) the parsley. Stir with a wooden spoon or spatula until a shaggy dough forms.
Turn the dough out onto a lightly floured surface and work in the additional flour (30-60g) until it's no longer sticky. Cover with a towel and let rise for 15-20 minutes.
Cut the dough into 10 portions and roll into balls. Sprinkle lightly with flour, cover, and let rest for 15 minutes.
Heat a cast iron skillet over medium heat.
While the pan is heating, flatten one of the dough portions into about a 7-inch circle. Repeat with the other dough.
When the pan is hot, brush one of the rounds with olive oil and place in the pan oiled side down. Lightly brush the top with oil. Cook for 60-90 seconds until the top is bubbly and bottom is golden. Flip and cook for another 60-90 seconds.
Repeat with the other flatbreads.