Oyster And Plantation Soup

• 2 ripe plantains see note
• 1 shucked oysters in their liquor (fresh)
• 350 ml cans unsweeteed cocnut milk
• 240 ml cream (heavy)
• 240 ml chicken stock
• 120 gr onion (chopped)
• 28 gr butter
• 8 gr all purpose flour
• 6 gr salt
• 5 gr garlic powder