Hake with piperonata and buttered crumbs

1.1kg hake, ling, haddock, grey sea mullet or pollock

salt and freshly ground pepper

15g  butter 

For the piperonata:

2 tbsp olive oil

225g onion, sliced

a clove of garlic, crushed

2 red peppers

2 green peppers

6 large tomatoes (dark red and very ripe) (use tinned if fresh are out of season)

salt, freshly-ground pepper and sugar

a few leaves of fresh basil

For the mornay sauce:

600ml whole milk

a few slices of carrot and onion

3 or 4 peppercorns

a sprig of thyme and parsley

50g approx. roux (25g melted butter mixed with 25g flour)

150-175g  grated Cheddar cheese or 75g grated Parmesan cheese

¼ tsp mustard preferably Dijon mustard

salt and freshly ground pepper

For the buttered crumbs:

25g butter

50g soft, white breadcrumbs

900g mashed potato (optional)