Prepare sirloin flap meat by trimming off fat. Cut the meat into 1-inch steak tip cubes. Set the meat aside.
Put the butter in a medium saucepan over medium heat. As the butter begins to melt, add the ketchup, mustard, Worcestershire, brown sugar, molasses, vinegar, Sazon, black pepper and lemon juice. Bring to a boil, then reduce heat to a low simmer. Cover the pot and simmer for 1 hour.
Remove the cover and add the cayenne pepper. Let the marinade simmer for another 20 to 25 minutes.
Remove the pan from the stove and cool the marinade for 2 1/2 hours.
In a large mixing bowl, combine the steak tips and sauce. Toss to make sure each piece is coated. Cover the bowl and refrigerate overnight for the sauce to soak into each piece.
Grill tips to desired temperature or doneness. Steak tips are best served with a tossed salad and roasted vegetables.
This recipe was provided by a chef, restaurant or culinary professional. It has not been tested for home use.