Bring a large saucepan 3/4 full of water to a boil. Add the fava beans and cook for 2 minutes. Drain and rinse immediately with cold water to stop the cooking.
NOTE: If you are using more mature fava beans in pods you may need to remove each bean's skin. Pinch each bean on the side opposite where it was attached to the pod. The bean should slip easily from the skin. Remove and discard the outer skins. Set the beans aside.
In a large saucepan with a tightfitting lid, heat the olive oil over medium heat. Add the onion and saute until soft and lightly golden, about 6 minutes. Add the garlic and saute for 30 seconds; don't let the garlic brown. Add the fava beans and stock and bring to a boil. Reduce the heat to low, cover and simmer, shaking the pan gently from time to time, until the beans are tender, about 15 minutes.
Season with salt and pepper. Sprinkle with the parsley and serve immediately.