Preparation

• Cut each steak in half (to get four steaks) and pat them dry with paper towels. Season both sides with salt and pepper.
• In a 12-inch heavy frying pan over medium heat, melt the butter with the oil. Add the onions, season with salt and pepper, and cook, stirring occasionally, until they’re well softened and translucent but not browned, 10 to 12 minutes. Transfer the onions to a large plate with a slotted spoon. If there isn’t much fat left in the pan, add another 1/2 Tbs. each of butter and oil.
• Increase the heat to medium high. Put the steaks in the pan and sear until deeply browned on both sides and  medium rare (cut into one to check), 2 to 3 minutes per side. Transfer to the plate with the onions.
• Pour the wine into the pan. As it comes to a boil, deglaze the pan juices by scraping the bottom of the pan well with a wooden spoon. Boil until it reduces to about 3 tablespoons, 2 to 3 minutes. Add the reserved onions and the steaks; pour in the marinara sauce and stir. Bring to a boil, reduce the heat, and simmer just until the onions are hot, 1 to 2 minutes. Garnish each serving with chopped parsley.