How to Make It
In a medium saucepan, toast the sesame seeds over moderate heat until golden. Add the Salsa Roja, stock, chocolate, raisins, cinnamon and nutmeg. Cook over moderate heat, stirring, until the chocolate has melted, about 4 minutes. Transfer the sauce to a blender and puree until smooth. Season with salt and pepper and return to the saucepan.
Brush each steak with 1 tablespoon of the mole sauce and let the steaks stand at room temperature for 1 hour.
Light a grill. Season the steaks on both sides with salt and pepper. Grill them over high heat for 3 to 4 minutes per side for rare to medium-rare meat. Transfer to a platter and let rest for 5 minutes.
Meanwhile, bring the remaining mole sauce to a simmer. Whisk in the butter, 1 tablespoon at a time. Serve the steaks with the mole sauce on the side.
Mexican chocolate, a sweet chocolate flavored with cinnamon, is sold at Latin markets and specialty-food stores.