Bake pretzels according to package instructions WITHOUT SALT. Cool completely.
Preheat oven to 250°F. Slice pretzels in half like bagels, then tear into bite-sized chunks along with the pretzel rolls.Arrange in an even layer on a large sheet pan and bake for ~1 hour, tossing every 15 minutes until pretzels are completely dry, like croutons. Remove from the oven and place in a large mixing bowl.
Increase oven temperature to 375°F.
Heat pan over medium heat, then add butter. When butter melts, add the sausage and cook until browned, using a wooden spoon to break it into crumbles.
When the sausage is mostly cooked through, add the carrots, onions, and celery. Sauté until onions are translucent and golden, but not brown or crispy.
Add sausage mixture to the pretzel pieces along with parsley, rosemary, thyme, sage, MSG, salt, and pepper. Mix and stir until evenly combined.
Add ¾ cup chicken stock and 1 tablespoon whole grain mustard to the pretzel mixture. Stir well until all the liquid has absorbed.
In a small bowl beat together ¾ cup stock and 1 large egg. Add to pretzel mixture and stir again to combine and evenly distribute all the ingredients.
Let mixture sit for 15-20 minutes. Check the pretzel pieces — if they’re still quite firm or have dry spots, add another ¼ cup chicken stock and mix again.Repeat as needed until all the pretzel pieces are hydrated.
Grease or butter a casserole dish. Add the pretzel mixture in an even layer and sprinkle pretzel salt over the top.
Cover loosely with aluminum foil and bake for 20 minutes at 375°F. Remove the foil, rotate the dish, and reduce oven temp to 350°F. Bake for another 20 minutes until deeply golden brown and crisp on top.If it seems dry, pour ¼ cup chicken stock over top and bake for another 5-8 minutes.
Let rest for 10 mins before serving.