How to Make It
Fill a large bowl with ice water. In a large saucepan of boiling salted water, blanch the fava beans for 1 minute. Transfer to the ice water, drain, then peel them.
In a small saucepan, heat 1 tablespoon of the olive oil. Add the garlic and cook over low heat until golden, about 2 minutes. Add the jalapeño and cook for 1 minute longer. Season with salt.
In a large skillet, heat the remaining 1 tablespoon of olive oil until shimmering. Add the fava beans and cook over moderately high heat, without stirring, until blackened, about 1 minute. Transfer to a serving bowl and season with salt.
Add the butter to the skillet and cook over moderately high heat until it just starts to brown, about 30 seconds. Add the shallot and cook over low heat until softened, about 3 minutes. Stir in the lemon juice and remove from the heat.
Add the garlic-jalapeño mixture and warm shallot vinaigrette to the beans along with the cheese and tarragon and toss well to coat. Season the salad with salt and serve.