In a large bowl, add the water and yeast. Cover and let sit for 10 minutes to activate the yeast.
Once the yeast is bubbly and foamy, add the olive oil, flour, and salt. Stir together until combined and the flour is well incorporated. The dough will be shaggy and very sticky. Cover and let rest for 15 minutes.
With wet hands, stretch and fold each corner of the dough up and over itself (for a total of 4 folds). Cover and let rest for 15 minutes.
Repeat the process of stretching and folding each corner of the dough up and over itself. Turn the dough over (seam-side down) and rub the surface of the dough with oil. Cover and refrigerate overnight, 12-18 hours (up to 3 days).
Grease a 9x13-inch pan with butter and add 1 tablespoon oil to the pan. Transfer the dough to the pan. Turn it to coat all sides in oil then place it seam-side down. Cover and let rise for 3-4 hours, until doubled in size.
Meanwhile, make the herb oil. Heat the oil in a small saucepan until it reaches 100-110°F. Remove from heat. Add the garlic and herbs de Provence. Stir and set aside to cool.
Drizzle half the herb oil over top of the dough and use your fingers to dimple the dough and spread it towards the edges of the pan. Cover and let rise for 45 minutes. Preheat oven to 425°F.
Spoon the remaining herb oil over top of the dough. Sprinkle with flaky salt, if desired.
Bake for 30 minutes, rotating the pan 180° halfway through baking. The bread should be deep golden brown and the bottom should be crispy.
Allow the bread to cool in the pan for 7 minutes. Remove the bread from the pan and finish cooling on a wire rack.
Notes
Storage: Store covered at room temperature for up to 3 days.