Set EGG for direct cooking at 650°F/343°C.
Grill steaks to desired internal temperature. Set aside and keep warm.
Reduce heat to 350°F/177°C. Heat butter and olive oil in Big Green Egg Cast Iron Skillet. Add mushrooms and cook about 4 minutes. Add whiskey to skillet; cook and stir 2 minutes. Add cream; cook about 5 minutes until sauce thickens. Add steaks to skillet to warm; sprinkle with chives and serve.