Place flour in a large bowl; season
Heat half the oil in 4.5 litre (18 cup) slow cooker on sear (high) setting. Coat beef in flour; shake off excess (reserve excess flour). Cook beef in batches, for 5 minutes each side, or until well browned. Remove from cooker. (This can also be done on the stove top and transferred to the slow cooker)
Reduce cooker to sauté (medium) setting. Heat remaining oil in cooker; cook onion, and garlic, stirring, for 5 minutes or until onion softens. Sprinkle with reserved excess flour; cook, stirring, for 3 minutes. Gradually stir in bourbon, then stock, cola, paste, honey and thyme; bring to the boil. (This can also be done on the cook top and transferred)
Return beef to cooker. Cook, covered on low for 8 hours. Discard thyme; season to taste.
Just before serving, make celeriac mash
Boil, steam or microwave celeriac and potato until tender; drain. Mash with butter and cream in a medium bowl until smooth; season to taste.
Serve celeriac mash topped with beef cheeks and sauce; sprinkle with extra thyme. Serve with steamed trimmed baby carrots and green beans or halved sugar snap peas, if desired.