2/3 cup (5 fl oz/160 ml) warm water (105°–115°F/40°–46°C)
1 package (2 1/2 teaspoons) active dry yeast
1/2 teaspoon sugar
2 cups (10 oz/315 g) bread flour, plus more for dusting
2 tablespoons extra-virgin olive oil, plus more for oiling
Kosher salt and freshly ground pepper
3 tablespoons unsalted butter
2 yellow onions, thinly sliced
1 tablespoon firmly packed light brown sugar
8 slices thick-cut applewood–smoked bacon, cut into strips
Cornmeal for dusting
1/4 lb (125 g) Gruyère cheese, thinly sliced
2 tablespoons chopped fresh thyme