How to Make It
Preheat the broiler or light a grill. On a large rimmed baking sheet, arrange the bread in a single layer and brush both sides with olive oil. Broil the bread 8 inches from the heat or grill, turning once, until lightly browned outside but still slightly soft inside, about 2 minutes.
In a large saucepan of salted boiling water, blanch the fava beans until bright green, about 1 minute. Drain and cool under running water. Pinch the fava beans out of their skins and transfer to a bowl. (You should have about 1 1/2 cups of peeled favas.)
In a food processor, combine 1 cup of the peeled fava beans with the ricotta cheese, heavy cream, garlic, crushed red pepper and 1 tablespoon of olive oil and pulse until nearly smooth. Scrape the mixture into a bowl and stir in the mint, basil and shallot. Season the fava pesto with salt and black pepper.
Spoon some of the fava pesto on each crostini and lay a piece of prosciutto on top. Spoon the remaining 1/2 cup of peeled fava beans on the crostini, garnish with shaved Parmigiano and grated lemon zest and serve.