WARNING: This part has to be done the day before you want to serve. Stir together all of the marinade ingredients in a nonreactive bowl. Place the roast in a nonreactive container (or large ziplock bag) and marinate overnight. The day before is also a good time to make the gingersnaps if, like me, you are using homemade.
The next day: Remove the meat and pour the marinade in the slow cooker. In a large skillet, quickly brown all sides of the meat in the canola oil. Add the meat into the slow cooker and turn on low for 6 hours.
During the last hour or so of cooking time: Start to make the dumplings. Bring a large pot of water to a rolling boil. In a large bowl, combine the cooled mashed potatoes and salt and the egg. Stir in the baking powder and add the flour in 1/2 cup increments until the it resembles a dough and the mixture holds its shape when molded (roughly 3 cups). Form into 2 to 4 inch balls. They should be able to hold their shape but not be too floury. Drop them into the water. They should sink, then rise to the surface when cooked through. Set aside.
During the last 1/2 hour of cooking time: Skim off any visible fat that may have risen to the top then add the gingersnaps and turn the heat to high.
After the time is up, shred the meat a bit with a fork or break it into pieces. Serve hot, with dumplings on the side.