Melt butter in a medium-size skillet over medium heat. Sauté onions until soft; stir in jalapeños, ketchup, sugar and liquid smoke. Bring to a boil then reduce heat to medium-low and simmer for an hour or until sauce has thickened to desired consistency.
Smoke pork shoulder in a hot smoker for 3 to 5 hours at 210 degrees F (internal meat temperature of 150 degrees F). Remove, and wrap in aluminum foil. Refrigerate overnight.
Remove excess fat from pork. Using two forks, shred remaining meat into a large bowl. Mix in barbecue sauce.
Brown 2 slices of buttered sourdough bread in a skillet or griddle over medium heat. Place a slice of cheese on each slice. Top with ? of pulled pork mixture, a second slice of cheese and another slice of bread. Turn sandwich over when bottom slice has browned and brown the other side.