Put a 10-inch skillet over medium-high heat. Add 1/4 cup of the oil, the garlic, rosemary or thyme, 1/2 teaspoon salt, and 1/8 teaspoon pepper and cook until you begin to hear a sizzling sound and the aromatics are fragrant, 1 to 2 minutes. Add the fava beans. Stir until the beans are well coated with the oil and aromatics and then add 1 cup of water. Bring to a boil, reduce the heat to medium, and cook until the water has nearly evaporated and the fava beans are tender, about 12 minutes. Add more water if the pan looks dry before the favas are done. Remove from the heat.

Transfer the fava mixture to a food processor. Add the remaining 1/4 cup olive oil and the lemon juice and purée until smooth, stopping to scrape the bowl as needed. Season to taste with more salt and lemon juice. Drizzle with a little olive oil before serving.