For the harissa, place the chillies with the rest of the harissa paste ingredients, excluding the oil in a food processor.
Blitz and then with the motor running add the oil in a steady thread until well-combined, lighter in colour and paste like.
Use immediately or store in a sterilized jar with a layer of oil on top to seal.
For the ciabatta, mix 3 tablespoons of the harissa with the softened butter and stir well to combine.
Spread the harissa butter over both sides of the ciabatta.
Tear over the mozzarella and grill in the oven until the cheese has melted approximately 5 minutes.
Remove from oven, slice and transfer to serving board.
Sprinkle with herbs.