Grease bottom and sides of a 9x9-in. baking pan with butter.
Combine beef, onion, garlic, pepper, cilantro, adobo, oregano, vinegar and sazón in a medium mixing bowl. Mix well.
Preheat a large skillet or frying pan over medium-high heat until the rim of the pan is hot to the touch. Add the olive oil and heat for an additional minute. Add meat mixture and cook until beef is brown and all of the juices bubble up.
Add bay leaves, olives, raisins and tomato sauce. Mix and simmer for 10 minutes; set aside.
Preheat oven to 350°F/180°C.
Heat a large frying pan with vegetable oil, just enough to coat the bottom. Fry plantains for 2 - 3 minutes on each side or until golden and slightly crispy. Drain on a plate covered with a paper towel; set aside.
To assemble the pastelón, place a layer of plantains in the prepared square pan. Add a layer of the beef mixture then a handful of cheese; repeat. You want to finish with cheese and plantains.
Beat 3 eggs with the milk; pour over the pastelón. Let it sit for a minute, allowing the egg to soak in. Top off with just a bit more cheese.
Bake in oven for 20 minutes.