Thanks to FloatingKitchen for this recipe!
1 package (2 1/4 tsp.) active dry yeast
1 cup warm water, 90-105 degrees Fahrenheit
1 cup whole milk, at room temperature
About 1/2 cup extra-virgin olive oil, divided
1 tablespoon plus 1 tsp. kosher salt, divided
3 tsp. fresh rosemary, chopped and divided
3 tsp. fresh thyme leaves, chopped and divided
6 cups all-purpose flour
1 tablespoon butter
1 large onion, peeled and thinly sliced
2 medium shallots, peeled thinly sliced (about 1 cup)
1 tablespoon balsamic vinegar
2 cups red seedless grapes
1 tsp. sugar
Add the yeast to the bowl of your stand mixer and pour the warm water on top. Let it sit for 5-8 minutes. Then add the milk, 1/4 cup of the olive oil, 1 tablespoon of the kosher salt and 2 tsp. each of the rosemary and thyme.
With the dough hook attachment, start mixing on low speed and gradually add in the 6 cups of flour. Once the flour is incorporated, beat on medium speed for about 10 minutes. The dough should be smooth and elastic. If your mixer can’t handle the job you can knead the dough by hand on a lightly floured counter top.
Cover the dough loosely with a towel and let it rise at room temperature in the bowl of your mixer for 1 1/4 – 1 1/2 hours. If your kitchen is chilly, find a warm spot in your house to let the dough rise. The dough should approximately double in size during this time.Using about 1 tablespoon of the olive oil, grease a rimmed baking sheet. I used a 10 X 15-inch pan. A larger 12 X 17-inch pan can also but used, resulting in a slightly thinner focaccia.
Punch down the dough and transfer it to your greased baking sheet. Using your hands, push the dough out into an even layer, stretching it all the way out to the rim. If the dough is especially springy, let it rest for about 10 minutes before continuing to stretch it out. Cover the dough loosely with a towel and let it rise for 45-60 minutes.Meanwhile, pre-heat your oven to 425 degrees. Caramelize the onions. Heat a large skillet over low-medium heat. Warm 2 tablespoons of the olive oil and melt the butter. Add the sliced onions and shallots, stirring to coat them in the fat, then sprinkle with 1 tsp. of salt. Cook for about 15-20 minutes, stirring occasionally, until softened and browned.
Stir in the balsamic vinegar and cook for 1 minute more. Then remove from the heat and set aside.With your fingers, poke holes on the surface of the risen dough. Spread the caramelized onions evenly over the top of the dough. Then scatter the grapes over top. Drizzle about 2 tablespoons of olive oil over everything. In a small bowl, combine the remaining 1 tsp. of rosemary and thyme with the sugar, then sprinkle them evenly on top of the dough.
Transfer the focaccia to your pre-heat oven and bake until golden, about 25-30 minutes. Remove from the oven and set aside to cool for about 15 minutes. Then using a large, wide spatula, loosen and slide the focaccia out onto a cutting board. Slice and serve warm or at room temperature.