Melt the butter in a medium-sized saucepan, stir in the flour, and heat the mixture briefly, making sure it doesn't start to brown. Gradually add in the milk, stirring continuously, then bring the béchamel sauce to a boil. Season the sauce with salt & pepper, then remove it from the heat and let it cool down.
Fry the ground beef in a small amount of vegetable oil and season it with salt & pepper.
Peel and slice the onions, then caramelize them in vegetable oil until they become golden brown.
Stir together the caramelized onions, cooked ground beef, béchamel sauce, and sliced jalapeños.
Grease a 10-inch bundt cake pan, then spoon about ⅔ of the onion mixture into it. Press the cheddar cheese cubes into the onion mixture, then fill up the bundt cake pan with the remainder of the onion mixture. Transfer the bundt cake pan to the freezer and freeze the stuffed onion ring for 3–4 hours.
Position the strips of bacon in a large circular pattern on a piece of parchment paper. Remove the stuffed onion ring from the freezer and place it in the center of the circle of bacon. Wrap the pieces of bacon around the onion ring until it's completely coated.
Set up the breading station with separate baking trays for the flour, whisked eggs for the egg wash, and bread crumbs. Coat the stuffed onion ring in flour, dredge it in egg wash, and cover it with bread crumbs. Then dip the breaded onion ring in the egg wash and coat it with bread crumbs a second time.
Preheat the oven to 325°F. Fry the giant onion ring on both sides until golden brown, then place it on a baking tray, transfer the baking tray to the oven, and bake at 325°F for 15 minutes.