1.Process onion, celery and garlic until chopped finely.
2.Heat 1 tablespoon of the oil in a large heavy-based saucepan or deep frying pan over medium heat. Add speck; cook for 5 minutes or until starting to crisp. Add onion mixture; cook, stirring, for 5 minutes or until softened but not coloured.
3.Add flour; cook, stirring for 1 minute. Add nutmeg and milk, stirring to combine well. Add potato and stock; bring to the boil. Reduce heat to low; cook for 5 minutes.
4.Stir in clams; cook, covered, for 4 minutes or until opened. Add prawns, fish and scored calamari pieces; cook for 3 minutes. Add scallops; cook for a further 1 minute. Stir in cream until heated through.
5.Heat remaining oil in a small heavy-based frying pan over high heat. Cook reserved calamari tentacles for 1 minute or until a little crisp.
6.Divide chowder among bowls; top with calamari tentacles and scatter with fresh herbs. Serve with grilled bread.
Pot-ready clams have already had sand purged from them and require no preparation. To purge clams yourself, place them in salted water (allow 30g/1oz sea salt to 1 litre/4 cups cold water) for several hours, then remove from water carefully; do not drain in a colander as you may add the sand back to the clams.
Instead of swordfish, use another firm oily fish, such as kingfish or marlin.