Season the shanks well with salt and pepper.
Heat the butter and oil in a cast-iron pot and brown the shanks.
Remove from the pot and set aside.
In the same pot, sauté the onions and celery until soft.
Add the cake flour and heat for a few minutes, stirring continuously.
Add 250 ml of the white wine, bring to the boil and cook until the liquid has reduced by half.
Add the stock, parsley and oregano.
Return the meat to the pot, cover and simmer slowly for 2 1/2 hours or until the meat is tender (add more white wine if the pot seems dry).
Remove the meat from the pot.
Beat the lemon juice and egg yolks with 125 ml of the meat sauce.
Remove the pot from the heat and stir the egg yolk mixture into the sauce.
Return the meat to the pot and mix.
Serve with mealie meal porridge