Focaccia with Caramelized Onions and Roasted Red Peppers

Name: Focaccia with Caramelized Onions and Roasted Red Peppers
Cuisine: European, Italian, Mediterranean
Ingredients: 290 grams bread flour (2 1/4 cups); 150 milliliters lukewarm water (2/3 cup); 60 milliliters extra virgin olive oil (1/4 cup); 7 grams kosher salt (2 teaspoons); 6 grams instant yeast (2 teaspoons); 30 grams unsalted butter (2 tablespoons); 2 medium onions, peeled and sliced into thin rings (about 200 grams sliced onion); 120 milliliters olive oil (1/2 cup), divided; 80 grams jarred roasted red peppers, drained and sliced into strips ( 1/2 cup); 60 grams whole black olives, drained and pitted (1/2 cup; about 15-20 olives); Flaky sea salt, for sprinkling