Preheat the oven to 350°. Spread the pine nuts in a pie plate and toast for about 6 minutes, until fragrant and lightly golden.
In a large bowl, whisk the mayonnaise with the vinegar. Slowly whisk in the olive oil until incorporated. Add the chives and season with salt and pepper. Add the watercress, endive and pine nuts to the bowl and toss to coat. Serve at once.