Fry onion and celery in olive oil and butter for 8 minutes until soft.
Add bay leaves and thyme to the vegetable mixture.
Steam clams in 570ml of simmering water for 3 minutes until shells open.
Drain clams while reserving the liquor and discarding unopened shells.
Combine sweetcorn, clam liquor, and chicken stock with the onions and simmer for 12 minutes.
Add potatoes and cook for 10 minutes until soft.
Stir in clam meat, cream, and parsley; cook for 5 minutes and season.
Pulse bread into crumbs and fry in oil with lemon zest and thyme until crisp.
Fry pancetta slices in oil for 3 minutes per side until golden.
Serve soup in bowls topped with breadcrumbs and crisp pancetta.