Heat the olive oil in a frying pan. Add the nettles and cook for 1 min until wilted. Allow to cool for 1 min, then roughly chop. Add to a bowl with the crème fraÎche, mustard and half the blue cheese. Stir in seasoning and set aside.
Heat the grill and lightly toast the bread on both sides. Divide the nettle and cheese mix between the toasts then pile on the remaining cheese and grill until golden and bubbling. Serve immediately.