Broil beef fillets according to preference.
Meanwhile, poach shucked oysters in their liquid just until tender.
Remove oysters and reduce liquid to a glaze over medium high heat.
Add butter to the pan and melt.
In a small bowl beat together cream and egg yolk.
Add a little hot glaze to egg-yolk mixture.
Add egg-yolk mixture and oysters to pan; blend well until slightly thickened over low heat.
Serve oyster sauce over beef.