Remove the shells off the prawn and heads too. Dice the prawn meat and put aside. Place the heads and shells into a pan with the butter, garlic and onion until lightly browned. Splash in the white wine and evaporate followed by 1 litre of hot water and bring to the boil. Season well with salt and pepper, lower the heat and simmer for 45minutes. Allow to cool slightly then blend into a prawn bisque and strain. Place the prawn bisque back into a pan, whisk in the, milk powder and a knob of butter and reheat gently. Meanwhile, heat a drop of oil in another pan and quickly cook the salmon and prawns till cooked. Serve the prawn and salmon mixture into deep soup bowls and pour the bisque on top. Garnish with fresh dill and serve.