Salt and pepper both sides of the steaks. Grill in 2 tablespoons butter until medium rare.
Saute onions in 4 tablespoons butter over high heat. Cook for 5 to 7 minutes, or until dark and caramelized. Reduce heat to simmer and pour in cream. Cook for 3 to 5 minutes, or until reduced by half. Stir in blue cheese until melted.