I use a 12" deep cast iron skillet with lid for this.
Heat butter and olive oil in skillet on medium heat. Now turn heat to med-high. Brown steaks on all sides. Reduce heat to low. Top steak with mushrooms. In a mixing bowl add all ingredients (but not the flour). using a wisk,wisk till well mixed.
Pour over steak,cover and simmer for 2 hours.or untill meat is tender.(If you need to add liquid while cooking.I added 1/2 cup of beef stock).