Combine spices of marinade together in a cheesecloth or mesh bag. Add to a non-reactive bowl with the apple cider and red wine vinegar.
Cut the beef roast into large slices. Place in the non-reactive bowl with the marinade and refrigerate overnight or for at least 12 hours, but up to 3 days.
Pour the liquid of the marinade into a 6 quart or larger slow cooker. Discard the spices.
Add carrots and onion to the slow cooker.
Over medium high heat, quickly sear the marinated beef for a minute on each side, then transfer to the slow cooker.
Cover and cook on low for 6-8 hours.
Gravy - *see notes at bottom
Put gingersnap cookies into a food processor and pulse until smooth.
30 minutes before sour beef is done cooking, remove 1 cup of the liquid from the crockpot and place into a saucepan. Over low heat, stir in the gingersnaps and continue to whisk until dissolved and thickened, about 5 minutes.
Set the gravy aside, or pour into the slow cooker and stir until combined with beef and vegetables.
Prepare dumplings 15 minutes before serving meal.
Combine prepared mashed potatoes with egg and salt, then mix in flour and baking powder until a dough forms. You may need additional flour. Mix until they're tacky but not sticky.
Bring 6 cups of water to a boil and drop in the dumplings. Cook for 2 minutes and when they float back to the top, remove with a slotted spoon and set aside.
Shred the beef using two forks. Spread beef and vegetable mixture onto a plate and place dumplings to the side. Garnish with fresh parsley if desired.
THE BEEF NEEDS TO MARINATE OVERNIGHT OR FOR AT LEAST 12 HOURS, PLEASE PLAN ACCORDINGLY. Marinade: pickling spice may be used in place of the marinade spices. Make sure to use a cheesecloth or mesh bag to hold the spices. Dumplings: you can use prepared mashed potatoes for this recipe to make it quicker. If making from scratch, make them early and let them cool completely. You may need more or less flour, depending on how moist your mashed potatoes are. Gravy: You do not need to cook the gravy separately. You can stir crushed gingersnap cookies directly into the slow cooker when there is 30 minutes remaining. It will thicken on its own.