How to Make It
Preheat the oven to 350°. Spread the pistachios on a large rimmed baking sheet and toast for 8 minutes. Let cool. Transfer the pistachios to a food processor and pulse until coarsely ground.
Meanwhile, in a small bowl, soak the shallot in the vinegar for 10 minutes. In a large bowl, whisk the mayonnaise with the lemon juice and garlic. Gradually whisk in the olive oil until thickened.
Drain the shallots and stir them into the mayonnaise along with the crème fraîche, parsley and tarragon. Stir in the ground pistachios and season with salt and pepper. Scrape the dip into small bowls and serve with the crudités.