In a mixing bowl, combine the flour, salt, and yeast. Gradually add warm water and olive oil, mixing until a dough forms.

Knead the dough on a floured surface for about 5-7 minutes until smooth and elastic.

Place the dough in a lightly oiled bowl, cover with a damp cloth, and let it rise in a warm place for about 1 hour or until doubled in size.

In a skillet, melt the butter over medium heat. Add the sliced onions and cook, stirring occasionally, until caramelized, about 15-20 minutes.

Season with black pepper and sea salt, then remove from heat and set aside.

Preheat a skillet or griddle over medium-high heat.

Divide the risen dough into 4 equal portions. Roll each portion into a flat circle about 1/4 inch thick.

Place the rolled dough onto the hot skillet and cook for about 2-3 minutes on each side until golden brown.

Top each flatbread with the caramelized onions while still warm.