In a large mixing bowl, combine the active sourdough starter, warm water, olive oil, sugar, and salt. Stir until smooth.

Gradually add the flour while mixing until a shaggy dough forms.

Transfer the dough to a lightly floured surface and knead for 8–10 minutes until smooth and elastic.

Place the dough into a lightly oiled bowl, cover with a damp towel, and let it rise for 3–4 hours, or until nearly doubled in size.

While the dough is rising, mix together mozzarella, cheddar, garlic powder, black pepper, and chopped parsley. Set aside.

Turn the risen dough onto a lightly floured surface. Divide it into 6 equal pieces. Roll each piece into a smooth ball. Cover and let them rest for 15 minutes.

Roll one dough ball into a very thin circle, about 10 inches wide. Brush the surface generously with the melted butter and olive oil mixture. Sprinkle an even layer of the cheese mixture over the dough. Fold the dough like a letter, then fold again to create layers. Gently roll it into a round flatbread about 7–8 inches wide. Repeat with the remaining dough.

Heat a cast-iron skillet or heavy frying pan over medium heat. Place one flatbread into the dry skillet. Cook for 3–4 minutes until golden brown. Flip carefully. Cook the other side for another 3–4 minutes until crisp and the cheese has fully melted. Brush lightly with melted butter after cooking. Repeat with the remaining flatbreads.

Sprinkle with fresh parsley, grated Parmesan, or red chili flakes if desired. Serve warm while the cheese is stretchy and melty.