How to Make It
Preheat the oven to 425°.
In a medium mixing bowl, toss the fennel with 1 tablespoon olive oil and 1/4 teaspoon salt. Arrange in an even layer in a large cast-iron skillet. Roast in the oven until browned and caramelized, 35 minutes. Set aside and wipe the pan clean.
Meanwhile, in a medium mixing bowl, whisk the chickpea flour and 1 teaspoon salt together until incorporated. Slowly whisk in 1 cup of lukewarm water. Stir until the liquid is absorbed and the batter is smooth. Allow to sit, covered, until the fennel is done. When ready to bake, stir in 2 tablespoons of olive oil.
Increase the oven temperature to 450°. Add 2 tablespoons of olive oil to the hot skillet. Pour in the batter and swirl the pan so it forms an even layer. Bake the flatbread for 10 minutes, until the center is firmly set. Remove from the oven and top with the fennel and Manchego. Return to the oven until the cheese is melted and beginning to brown, 5 minutes. Cut into wedges and serve the socca immediately.