Place the cubed beef roast in the slow cooker and cover it with diced onion.
In a medium bowl, mix together the dry mustard, sweet paprika, salt, brown sugar, Worcestershire sauce, and ketchup.
Add 1 cup of water to the mustard mixture and pour it over the onions and beef in the slow cooker.
Cover the slow cooker and cook on low for 9 to 10 hours or until the meat is tender.
About 30 minutes before serving, mix approximately ¼ cup of water with the all-purpose flour to make a paste.
Stir this paste into the goulash in the slow cooker.
Increase the heat to high and cook for an additional 10 to 15 minutes, or until the sauce thickens.
Serve the slow cooker Hungarian beef goulash hot over rice or spaetzle.
Notes / Tips / Wine Advice:
Wine Advice:
This hearty dish pairs well with a full-bodied red wine such as a Cabernet Sauvignon or a Merlot. The rich flavors of the beef and the savory sauce are complemented by the bold and robust characteristics of these wines. If you prefer a white wine, opt for a dry Riesling or a Chardonnay with some oak aging to stand up to the richness of the goulash.