For the marinade: Season the beef on all sides with salt. Place in a large plastic bag (turkey bag!) and add the onions, red wine vinegar, pickling spice blend, honey, peppercorns and 1 cup water. Marinate, refrigerated, for 2 days.
For the sauerbraten: Remove the beef from the marinade and reserve the marinade. Pat the beef dry. Sprinkle the flour on all sides of the beef. In a large pan on high heat, add the oil. When it begins to swirl and smoke, add the beef. Sear on all sides to a deep golden brown, 6 to 8 minutes; don't forget the ends!
Add the beef to a slow cooker and pour in the reserved marinade and red wine. Cook on low for 8 hours, until the meat is tender but not falling apart.
Remove the beef, tent loosely with foil and rest for 10 minutes. Turn the slow cooker to high and reduce the liquid slightly, 10 to 15 minutes.
Slice the beef and serve with the sauce, boiled potatoes and Sunny's Simple Red Cabbage Kraut.
To a large pan with straight sides or a stockpot, add the beer, sugar, vinegar, red pepper flakes, liquid smoke, garlic and peppercorns. Turn the heat to medium high and stir to dissolve the sugar. Stir in the onions and cabbage and bring the mixture to a boil. Turn down the heat and simmer, stirring occasionally, until the cabbage is tender, 35 to 45 minutes. Serve warm or chilled.