Preheat the oven to 160°C or 140°C fan-assisted (gas 3).
In a heavy based casserole dish over medium-high heat sear the
beef and onions until nicely browned, remove and keep to one
side.
Add the tomato paste, mustard, herbs and stout and reduce by
50% then pour over the stock, bring to a boil and thicken with the
corn flour mix before placing the beef and onions back in the
casserole dish.
Place in the oven covered and braise for approximately 3 hours,
until the beef is tender when pierced with a skewer.
Remove the beef & onions from the gravy, place on a warmed
deep serving dish and cover with foil to keep warm.
Reduce the gravy until you reach a rich sauce like consistency,
season to taste then pass the gravy over the beef and onions.
To serve
Serve with glazed baby carrots and mashed potatoes with parsley
and extra mustard at the table and a glass of your favourite
stout.