Put the cod in a large container and cover with cold water. Leave to soak at room temperature for 24 hours, changing the water at least four times.
Preheat the oven to 180C/200C Fan/Gas 4. Place the potato on a baking tray, wrapped in kitchen foil, and bake for 1¼ –1½ hours, or until cooked through. Keep the oven on. Once the potato is cooled, remove the flesh and pass it through a ricer. Set aside.
Meanwhile, bring a saucepan of salted water to the boil and add the artichokes and lemon juice. Cook for 25–30 minutes, or until the outer leaves are easily detached. Leave to cool then cut in half and remove some of the central leaves.
Place the salt cod in a shallow dish and add the milk, garlic, bay leaf and thyme. Leave to poach for 10 minutes, then remove and flake the fish into a small bowl and reserve the milk.
Stir in the potato, oil and some of the reserved milk. Season with salt and pepper and spoon the mixture into the artichoke. Sprinkle the breadcrumbs over the top and bake in the oven for 10–15 minutes, or until golden.
Whisk the lemon juice, oil and salt and pepper in a small bowl. Put the leaves in a large bowl and dress with the dressing.
Serve the baked artichokes on a serving plate with the dressed leaves scattered around the edge.