Melt half of the butter in a saucepan, and cook the onions in it until they are soft but not brown. Add the peas and milk. Simmer until the peas are just tender. Add the oysters and clam juice, and simmer over very low heat for 10 minutes. Put in the wine, remaining butter, salt, and pepper. When the butter melts, puree the mixture and beat, or whirl in the blender until light. Return to the saucepan. When ready to serve, preheat the broiler, and whip the cream seasoned with a little salt. Heat the soup almost to boiling, and spoon it into hot, heatproof dishes. Top each dish with a generous amount of whipped cream, and place under the broiler until cream is golden brown.