Cut Prime Rib or Tenderloin lengthwise within 1/2" from bottom. Place frozen lobster tails in boiling salted water. Boil for only 5 minutes. Carefully remove lobster with scissors, cutting down sides. Put in length wise end to end.
Mix: 1 tbsp butter
1 1/2 tsp lemon juice
Brush this inside meat before putting in the lobster and tie with string. Roast at 425 for 1/2 hours then turn down to 350 for 2 hours. Wrap Roast in foil and let sit for 1/2 hour before serving.
Meanwhile cook onions, butter and garlic salt until well heated. This feeds 8 people. This is nice served with salad, baked potatoes, small peas and garlic toast.