Using a large frying pay, melt 1 teaspoon of butter and brown the inside edges of the bun. (I've found this really helps to keep your bun from getting soggy!) Remove bun to a plate.
Prepare a patty from the ground chuck and grill or fry it until done to your liking.
In same pan, heat up the grilled onions and add the jalapeno slices to the pan to warm and soften a bit. I cooked my burger inside so did all three of these tasks at one time in the same pan.
When the burger, onions and jalapenos are done; remove them to a plate. Wipe out the skillet. Melt 1 tsp of butter in the center of the pan and put the bottom side of the bun on the butter.
Layer with sliced pepper jack cheese, then burger, onions, another slice of cheese and jalapeno pepper slices.
Mix the mayonnaise, stone ground mustard and hot sauce to taste in a small bowl. Spread the inside of the top bun with this mixture and then top the patty with the bun.
Heat on low to medium heat, covered with a lid or a piece of aluminum foil.
Once cheese has visibly melted on the bottom, remove the sandwich, melt another teaspoon of butter on the bottom of the pan.
Flip the patty melt over and continue heating until the cheese starts to melt pressing the burger to flatten it slightly. Remove the burger from the pan and cut in half to serve.