How to Make It
Blanch the shelled favas in boiling water for 1 minute. Drain, then rinse in cold water to stop the cooking; drain again. Pinch the favas out of their skins.
Preheat the oven to 350°. In an ovenproof skillet, heat 2 tablespoons of the olive oil over moderate heat. Add the favas, garlic, squash and zucchini; season with salt and pepper. Cook until just softened, 3 minutes. Transfer to a plate.
In a medium bowl, beat the eggs with the milk; season with salt and pepper. In the same skillet, heat the remaining 1 tablespoon of olive oil over moderately high heat. Pour in the eggs, then stir in the cooked vegetables, sorrel, peas, scallions and chives; season with salt and pepper. Cook the frittata over moderate heat until the edge is set, 2 minutes. Transfer the skillet to the oven and cook for 25 minutes, or until the frittata is set in the center and browned on top. Serve hot or at room temperature.