Bring a small pot of water to a boil. Boil fava beans 2 minutes, then drain in a colander and pour into bowl of ice and cold water. Skin each bean by tearing open at round end with a small knife and popping out the bean. Set favas aside.
Fill pot with fresh water, season with salt, and bring to a boil. Add peas and boil until just tender, about 2 minutes (taste one to check). Drain in a colander.
Meanwhile, put 3 tbsp. oil in a medium frying pan and heat over medium heat. Add the leeks and garlic and cook until tender but not browned, about 5 minutes. Add cooked favas and peas, season lightly with salt (keeping in mind that the ham will add saltiness), and stir to coat vegetables with oil. Heat until favas are warmed through, 1 to 2 minutes. Remove from heat and add ham. The heat of the pan will wilt it slightly.
Heat remaining 1 1/2 tbsp. oil in a large nonstick frying pan over medium-high heat. Crack eggs into pan and cook, basting tops of eggs every now and then with spoonfuls of hot oil, until they've developed a golden, crisp bottom but their yolks are still runny.
Spoon vegetables onto a platter and add watercress, herbs, and small dollops of crème fraîche, which will melt into the vegetables and create a little sauce. Top with fried eggs, season with salt if you like, and serve immediately.