Set slow cooker on sear mode.
Dust steak lightly with seasoned flour.
Heat oil in slow cooker and brown cheeks on all sides.
Remove and set aside on a plate.
Add butter to slow cooker and mix with the pan juices.
Add onions, carrots, celery, thyme and garlic and cook until onions are transparent.
Add red wine let it cook off for about 30 seconds.
Stir in extra flour and cook for 2 minutes.
Gradually add stock, stir until sauce boils and thickens a little.
Add Vegemite, tomato paste and Worcestershire sauce and stir to combine.
Put cheeks back into slow cooker and coat with the sauce.
Wrap the lid in a tea towel or slow cooker lid cover.
Cook on LOW for 4hrs or until cheeks are tender and just about to pull apart.
Remove cheeks to a plate.
Taste the sauce add salt & pepper if needed.
Mix 2 tbsp cornflour with a little water to make a runny paste.
Stir through the sauce, add the cheeks back to the sauce and let it cook for another 30 minutes.