Add onion to slow cooker bowl and sit the beef on top
Combine other 3 ingredients and spread this mix over the beef
Cook on low for approx 6hrs for 1kg piece, 8hrs for 2kg piece or until cooked through to your preference
Remove roast beef and allow to rest while you thicken the sauce
Reduce the cooking liquids/gravy on searing setting of your slow cooker or over stovetop for approx 5mins to thicken
Slice your roast beef (I get best results with electric knife if you have one) then serve with the lush rich gravy generously poured over your beef and your vegetables of choice
Notes
I slow cook my roast vegetables using the 'Roast Vegetable' recipe of mine on this website