French Onion Soup Focaccia

Instructions

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1. 1 For the focaccia: Pour water into a large bowl and sprinkle yeast and sugar on top. Mix briefly with a dough whisk or wooden spoon, then let sit until the yeast has bloomed, about 10 minutes. When ready, the top of the bowl should look like a foamy beer.
2. 2 Stir in olive oil and salt. Add all-purpose flour and bread flour and stir with the dough whisk or a wooden spoon until no dry streaks of flour remain.
3. 3 Cover the bowl and allow to rise for 45 minutes. After 45 minutes, uncover the bowl and wet your hands slightly. Starting at the top of the bowl, use your wet hands to pull the top edge of the dough up and over the dough ball. Continue this process until you work your way all around the dough. This is known as a stretch and fold. It helps to develop gluten and replaces traditional kneading. Cover the bowl again and let sit in a warm spot.
4. 4 After 30 minutes, repeat the stretch and fold process. Cover the bowl and perform two more sets of stretches and folds 30 minutes apart. After the 4th stretch and fold, cover the bowl and let sit for 30 minutes.
5. 5 At this point, the dough should have doubled in volume and be smooth to the touch. The dough is now ready to be used, or can be chilled overnight to use the next day.
6. 6 For the toppings: Lightly oil a 9x13-inch metal cake pan. Set the focaccia base in the pan, using your fingers to gently stretch it into all four corners. Cover the focaccia and let rise for about 1 hour.
7. 7 Meanwhile, melt butter in a light-colored skillet over medium heat. Add onions and a generous pinch of salt and cook over medium-low heat, stirring often until onions are deeply caramelized, about 40 minutes. As the onions cook, you may need to add water, 1/4 cup at a time, to keep the onions from burning. After 40 minutes, onions should be deeply browned and jammy in consistency. Remove from heat and set aside to cool slightly.
8. 8 Preheat the oven to 450 degrees F (230 degrees C).
9. 9 Lightly drizzle the surface of the focaccia with olive oil. Use your fingers to dimple the surface, then scatter Gruyère cheese in an even layer. Dimple the surface again, then dollop onions all over the surface. Sprinkle with herbes de Provence.
10. 10 Bake in the preheated oven until the focaccia and cheese are golden brown and bubbly, 25 to 30 minutes.
11. 11 Remove from the oven and let sit in the pan for about 10 minutes, then carefully slide focaccia onto a cutting board. Let cool for an additional 10 minutes before slicing and serving.