Season the pork butt generously with salt and pepper. Spray the inside of the slow cooker with cooking spray and pour in the Coke. Puree the stemmed maraschino cherries with their liquid in the blender until smooth. Add to the Coke and stir to combine. Add the pork butt and cook on low for 9 – 10 hours.
Remove the pork from the slow cooker and pour the cooking liquid into a large sauce pan. Add the ketchup, mustard and chipotle puree to the cooking liquid, stir to combine and bring to a boil over high heat. Continue to boil until the liquid has reduced by about half, about 10 minutes. Taste and add more salt and pepper if desired.
While the sauce is boiling, shred the pork with two forks and discard bone if there is one. Add the pork to the pot with the sauce and toss to coat. Keep warm.
Brush the cut sides of the hamburger buns with melted butter and cook on a hot skillet for a minute or two until toasted. Serve the hot pork on top of the toasted buns.
Notes
*to make chipotle puree, blend a can of chipotle in adobo sauce in the blended until pureed. Store in a covered container in the refrigerator and use as desired.