Light the BBQ and heat it to a temperature of 180 °C. Scrub the sweet potatoes, then dry them and place on a piece of aluminium foil.
Thinly slice the garlic. Remove the thyme and rosemary leaves. Mix the garlic and herbs with 2 tablespoons of olive oil. Brush the sweet potatoes with the herb oil. Wrap the aluminium foil around the sweet potatoes and place this package on the BBQ. Close the lid and bake the potatoes in approx. 35 minutes. The sweet potatoes are done when you can easily insert a fork.
In the meanwhile, finely slice the chives and mix with the clotted cream. Season with salt and pepper.
Trim away the woody base (2 cm) of the asparagus. Brush with the rest of the olive oil and sprinkle with salt and pepper. Place the asparagus on the BBQ and grill for approx. 3 minutes. Turn them halfway. Close the lid each time.
Carefully unwrap the foil from the sweet potatoes and halve them lengthwise. Divide the clotted cream over the potato halves and arrange 3 asparagus and an anchovy fillet on each half. Garnish with the watercress.
