In a large skillet, heat the remaining 3 tablespoons of olive oil until shimmering. Add the remaining 1 clove of garlic, then add the watercress, arugula, spinach, kale and endive. Toss over moderate heat until just wilted, about 40 seconds. Add the wine mixture, toss to coat and season with salt and pepper. Mound the salad in bowls, top with the croutons and serve.