Ingredients (for three burgers):
1lb ground beef ( the fattier the better, use 80/20 mix)
3 slices American cheese (melts better than unprocessed cheese)
Divide the ground beef into three more or less equal amounts and then further divide each of those amount into two balls. Smash each ball into a thin patty so that you now have six. If you try to make your burgers any smaller, there will not be enough meat to seal the other ingredients in side.
take one slice of cheese and tear into quarters.
Take one patty and place a jalapeno slice, about a teaspoon of caramelized onions, and stack the quartered cheese slice in the very center. Take a second patty and cover it. Pinch around the edges to to seal and check to ensure that the interior ingredients are completely enclosed (you don't want your cheese to leak out as it melts).
Heat a skillet over medium heat and then cook each burger approximately five to six minutes. Carefully flip and then cook another five to six minutes on the other side. This seems long for a burger, but it needs to get hot enough to cook all the way through and melt the cheese on the inside. It does take some experimenting with your particular cook top or grill. You will need high enough heat to sear the outside of the burger but low enough that it doesn't burn on the outside before the inside is thoroughly cooked.
Once cooked, serve immediately (before the cheese on the inside cools) on pretzel or rye buns. And be sure to have plenty of napkins.