pounds red, green or black seedless grapes (or combination)
cup + 2 tablespoons sherry vinegar
tablespoons unsalted butter, melted
bunches watercress, stems removed
Preheat oven to 450°F. Rub each chicken thigh all over with a piece of garlic clove. Place chicken thighs in large bowl and toss with 2 tablespoons olive oil; season with 1/2 of the salt and 1/2 of the black pepper. Transfer chicken to one side of a large, rimmed baking sheet.
In medium bowl, toss together grapes picked from the stems, sherry vinegar, butter and sugar. Season grape mixture with remaining salt and pepper. Spread grapes out on the other half of the baking sheet.
Place chicken and grapes in the oven and roast, tossing grapes occasionally with wooden spoon, until chicken skin is crispy and juices run clear when pierced with a fork, about 30 minutes.
In medium bowl, toss the watercress with remaining tablespoon of olive oil. Arrange watercress on a platter or on individual serving plates; place chicken on top. Spoon grapes over chicken and serve.