1.5 kgsalt cod, cut into pieces (see note)7garlic cloves3fresh bay leaves300 mlolive oil260 mlmilk1½lemons, juice only1½ tspfinely grated nutmeg60 gmunsalted butter, plus extra for greasing1large onion, thinly sliced1 kgEnglish spinach (about 8 bunches), trimmed, blanched, refreshed and finely chopped65 gm (1 cup)dried coarse breadcrumbs40 gm (½ cup)coarsely grated parmesanTo serve:lemon halves
Place salt cod in a large bowl and cover with cold water. Soak for 24 hours, changing water 3-4 times (see note). Drain, place cod in a colander and rinse under cold water. Transfer to a large saucepan with garlic and bay leaves, cover with cold water and bring to the boil over medium heat, then simmer over low heat until flesh flakes easily when touched (8-10 minutes). Cool in liquid and, when cool enough to handle (10-15 minutes), remove fish and garlic from liquid (discard bay leaves). Coarsely shred cod (discard bones and skin) using fingers. Finely chop garlic, add to salt cod and process in a food processor until coarsely chopped and well combined (2-3 minutes).
In separate saucepans, warm olive oil and milk over low heat. Add one-quarter of the olive oil to salt cod mixture and process to combine, then add remaining olive oil and milk in batches, processing until smooth and creamy. Add lemon juice, nutmeg and season to taste with freshly ground white pepper, process briefly to combine, transfer to a bowl and set aside.
Heat butter in a large frying pan over medium heat, add onion and sauté until soft (4-5 minutes). Add spinach and cook over low heat, stirring, until warmed through (6-8 minutes), then season generously with freshly ground white pepper.
Preheat oven to 200C. Lightly grease six 2-cup capacity ovenproof dishes. Divide half the salt cod mixture evenly, top with half the spinach mixture, then repeat with the remaining mixtures. Scatter breadcrumbs and parmesan over dishes and bake until golden (20-30 minutes). Serve warm with lemon halves.
Note You may need to soak the salt cod in cold water for longer than 24 hours, changing the water a few more times, depending on how heavily salted it is.