Using cooking string, gently tie the shanks around the middle to hold them together. Season with salt and pepper.
In a shallow dish, add flour and dredge each shank lightly before removing any excess
Add 3/4 s of the oil to a large heavy bottomed skillet over a medium high heat.
When the oil is hot, sear the shanks until browned (3 - 4 minutes) per side. When each shank is seared, transfer to a large baking tray. I has to be large enough for all 6 shanks.
Drain the fat from the pan into a container and return the skillet to a medium heat. Add the remaining 1/4 oil and the butter to the pan and melt.
Once the butter is melted, add the celery, onion oregano, carrot and 1 tsp of salt. Cook for about 15 minutes until the vegetable have softened and slightly brown.
Then add the wine and increase the heat to a medium high and stir making sure deglaze any good bits stuck to the bottom of the pan. Heat until the wine has reduced by at least a third.
Add the tomato paste/puree and stir. Add the canned tomatoes including the juice and stir.
Add the stock/broth, bay, thyme and a few pepper grinds. It can take the pepper.
Increase the heat to medium high and bring to a boil Carefully pour the pan contents over the shanks in the baking tray.
Using tin/aluminium foil, cover the shanks and the tray making a tight fitting lid.
Place the shanks into the oven to braise making sure to check the liquid level regularly. If it has reduced below half the height of the shanks, add a little more chicken stock to top up. Cook for 1 1/2 - 2 hours.
To test the shank, pierce it with a fork and the meat should fall apart. Give it a taste. It should be soft, moist and tender.
When cooked to your liking, transfer the shanks to warmed dishes.
Strain the juices through a medium mesh sieve pushing every bit of juice and goodness through. Add half of the gremolata to the sauce and mix.
Return the now strained sauce to the heat and bring to a simmer. This will help to thicken the sauce.
In a small bowl, add the garlic, parsley, anchovies and lemon zest and mix thoroughly.
Serve the Osso Buco on warmed dishes with seasonal vegetables and pasta. Sprinkle the remainder of the gremolata over each dish.