Soak the fish in cold water for 24 hours, changing the water frequently. Drain the fish well. Cut the fish into pieces, place in a shallow pan and pour enough cold water to cover. Heat the water until it is simmering and poach the fish for 8 minutes, until it is just cooked. Drain the fish, then remove the skin and bones.
Combine the extra virgin olive oil and crushed garlic cloves in a small pan and heat gently. In another pan, heat the double cream until it just starts to simmer.
Put the cod into a food processor, process it briefly, then gradually add alternate amounts of the garlic flavored olive oil and cream, while continuing to process the mixture. The aim is to create a puree with the consistency of mashed potatoes.
Season to taste with freshly ground black pepper, then scoop the brandade into a serving bowl or onto individual serving plates and serve with the crispbread or crusty bread.