1 (3 1/2-pound) boneless pork shoulder roast

2 tablespoons oil, plus more for frying
1 yellow onion, thinly sliced
5 garlic cloves, peeled and smashed with the side of a knife
4 ounces sliced ham, cut into thin strips
1 cup dill pickle relish
2 cups shredded Swiss cheese
1/4 cup Dijon mustard, plus 2 tablespoons for dipping
2 tablespoons mayonnaise, plus 1/2 cup for dipping
12 egg roll wrappers
1 egg, beaten
Salt, pepper and ground cumin
Heat oven to 300F.
Season pork on all sides with salt, pepper and cumin. Heat oil in a Dutch oven over medium heat. Sear pork on all sides until brown, about 3 minutes a side.
Add onions and garlic to pan, then pour chicken stock over. Cover and place in oven until tender and falling apart, about 3 hours. Let cool until cool enough to handle, then shred meat into a mixing bowl. Add ham, relish, cheese, 1/4 cup mustard and 2 tablespoons mayonnaise and mix well. Season lightly with salt and pepper.
Lay a wrapper diagonally on a work surface and spread a line of filling across the center, leaving about an inch on either side. Brush the exposed surface with egg, then fold the top point over the filling. Fold in the sides, then roll up to enclose the filling. Repeat with remaining wrappers.
Heat oil to 350F. Fry egg rolls in batches until dark golden and crisp, about 4 minutes. Stir together remaining mayonnaise and mustard and dip hot egg rolls in the sauce.