In a saucepan, combine spaghetti sauce, wine, broth, pumpkin pie spice, chocolate and red pepper flakes. Bring to a boil over medium-high heat, stirring occasionally. Reduce heat to low and simmer for 30 minutes.
Season the steak generously on both sides with salt and pepper, patting the seasoning into the meat.
Heat a heavy skillet, preferably cast iron, over medium heat until hot. Add vegetable oil. When melted, add the steaks and cook until seared and well-crusted on 1 side, about 4 minutes. Add 1 tablespoon of butter to first side of steaks. Turn, add 1 tablespoon of butter to the other side of the steaks and cook 3 minutes more for medium-rare, and 4 minutes more for medium. Remove from the heat and let steaks rest for 5 minutes before slicing.
Slice steaks, place on plates, and spoon sauce over.
