Open oysters with an oyster knife, loosen meat and take it out, collecting all juice carefully. Rinse shells thoroughly, pat dry and place on coarse salt in an ovenproof dish.
Combine fish stock with oyster juice and bring to a boil. Poach oysters for 3 seconds, remove and place into shells. Reduce fish stock in half, add cream and season with salt and cayenne pepper. Cook hollandaise sauce according to package instructions and fold into sauce. Pour souce over oysters with a spoon.
Place oysters under a broiler for about 3 minutes or until golden brown, watching carefully. Remove from oven and top each oyster with a a pinch of caviar, garnish with dill and serve immediately.