Sautéed Mushroom and Caramelized Onion Focaccia
One Half-Sheet Pan (13” by 18”) Focaccia
Dough:
2 ¾ cup warm water (or I use 2 ¼ cup water and ½ cup of my sourdough starter)
1 Tbsp granulated sugar
4 tsp active dry yeast
3 ½ cups bread flour
3 cups all-purpose flour
1 Tbsp fine sea salt
Zest of one large lemon (save the lemon to squeeze over the focaccia when you remove it from the oven)
1/3 cup good olive oil – plus more for preparing the dough to bake and finishing
Flaky sea salt (to taste)
Topping:
2 medium yellow onions, peeled and thinly sliced
3 medium red onions, peeled and thinly sliced
1 quart mixed fresh mushrooms, thickly sliced
8 Tbsp unsalted butter
1 Tbsp fresh thyme leaves, lightly chopped
Fine sea salt and black pepper to taste
1 Tbsp balsamic vinegar
1) In a 4-cup glass measuring cup, stir together the warm water and the sugar. Sprinkle the yeast over the mix and then whisk until yeast is fully dissolved. Set aside to bloom for five minutes.
2) In a standing mixer, whisk together the two flours, salt and lemon zest. Stir the oil into the bloomed yeast mixture and then slowly pour the wet into the dry with the mixer on low. When the mixture starts to gather into a dough, increase the speed to medium and mix for 4-5 minutes until you have a smooth, soft and silky dough.
3) Oil a large glass bowl and turn the dough into the bowl, turning the dough to make sure it is fully covered with oil. Cover the bowl with plastic wrap and set aside until doubled in volume (about 45 minutes).
4) In a cast iron skillet, slowly cook, over medium high heat, the thinly sliced onion in 5 Tbsp of the unsalted butter until the onions are very soft and caramelized. Remove the onions to a medium bowl. Add the remaining 3 Tbsp of butter to the skillet and sauté the mushroom until they just give up about half of their moisture but still remain firm. Add the cooked mushrooms to the onions, folding them together. Add the fresh thyme leaves, the balsamic vinegar, and then salt and pepper to taste. Set aside.
5) Line your baking sheet with parchment paper and turn the dough onto the pan. Gently stretch the dough to evenly fill the pan. Use your fingers and deeply dimple the dough all over. Pour another 3-4 Tbsp of oil over the dough and evenly spread it over the dough with your hands. Cover the dough with plastic wrap and set aside for 30 minutes while your oven heats to 450 degrees.
6) Unwrap the dough. Dimple the top with your finger again. Evenly spread the mushroom/onion mixture over the dough, pressing it into the dough with your fingers. Sprinkle the top generously with flakey sea salt and bake for 20-25 minutes until golden brown. Remove from the oven. Squeeze the lemon over the hot focaccia and brush with even more olive oil. Transfer the focaccia to a wire rack and leave to cool.
