Simmer the Chile con Carne in a small skillet until hot. Add beef stock to thin it out if necessary.
Prepare the toppings. Shredded the cheddar, chop the onions, and slice the jalapeños.
Add a pat of butter to each side of the buns.
Toast the buns on a hot comal or skillet.
Remove the toasted buns and set aside.
Add remaining butter to a skillet. Bring up to high heat.
While the skillet is heating, add the onions to the melted butter and sauté just until soft.
Remove the sautéed onions, and set aside.
Form ¼ pound meatballs.
Add meatballs to the hot skillet. Cover with parchment paper.
Smash each meatball down hard for 10 full seconds. Cook the patties without moving for 3 minutes.
Salt and pepper the patties.
Flip the patties, pressing down hard with the skillet to scrape all of the browning from the pan.
Add the shredded cheddar.
Remove the patties and rest on paper towels.
Add the grilled onion, and sliced jalapeños to the top of the patty.
Plate the buns. Ladle chili over the bottom bun.
Add the burger patty and the top bun. Serve with a fork and knife.