1 cup chickpea flour
1 teaspoon kosher salt, divided
1 teaspoon freshly ground black pepper
1 cup lukewarm water
6 tablespoons olive oil, divided
1 small red onion, thinly sliced
1/2 cup diced butternut squash
1/2 cup diced cremini mushrooms
1 large clove garlic, minced
2 teaspoons chopped fresh rosemary
Crème fraîche mixed with lemon zest and minced parsley, for garnish
Put a 10-inch cast-iron skillet or nonstick pizza pan in the oven and heat to 450°.
In a medium bowl, combine the flour, kosher salt, and black pepper. Slowly add the water, whisking to eliminate lumps. Stir in 2 tablespoons olive oil. Cover the batter, which should have the approximate consistency of heavy cream, and let sit for at least 30 minutes.
Meanwhile, set another skillet on the stovetop over medium-high heat and add 2 tablespoons olive oil. Add the onion, butternut squash, and cremini mushrooms and cook, stirring, until the squash is just tender, about 5 minutes. Add the minced garlic and rosemary and cook until the squash is fully tender, 2 minutes more.
Remove the skillet from the oven and pour the remaining olive oil into it; swirl to coat. Gently fold the vegetables into the batter and quickly add to the pan. Bake until the pancake is set and the edges are brown, 10 to 15 minutes. For better browning on top, set under a broiler for a minute or two. Serve with a dollop of the herbed crème fraîche.