How to Make It
In a small saucepan, boil the vinegar with the shallot until evaporated, 3 minutes. Add the cream and simmer over moderate heat until reduced by half. Remove from the heat. Whisk in 4 tablespoons of the butter, 1 tablespoon at a time; return to the heat when the sauce gets cool but do not boil. Season with salt and cayenne.
In a small bowl, whisk the truffle juice, soy sauce and lemon juice with the olive oil; season the vinaigrette with salt.
In a large skillet, heat the remaining butter. Add the shrimp, season with salt and cayenne and cook over moderate heat, turning, until pink and curled; remove from the heat.
Arrange the mesclun on plates. Top with the enoki, tomato and avocado and drizzle with the vinaigrette. Whisk the butter sauce over moderate heat until very warm. Arrange the shrimp on the salad and drizzle with the warm butter sauce. Sprinkle with the chives and serve.
Porcini water can be substituted for the truffle juice; soak a few dried porcini in very hot water for 10 minutes, then strain.