Place a small (15-16cm or 6") saucepan over a high heat, add the wine and reduce by half. This will take approximately 15 minutes.
Bash the garlic cloves (Don't bother peeling them) and throw them into the wine whilst it is reducing.
Once the wine has reduced, pour in the tomato passata and lamb stock, then bring it to a simmer, then turn off the heat.
Whilst the sauce is coming to a simmer, heat a 28cm or 11" deep-sided frying pan over a high-medium heat. When the pan is hot, add the oil.Season the lamb with the salt and pepper, place them in the pan and sear until nicely coloured on one side.
Flip the lamb and add the butter and anchovies, and cook for two minutes, basting the top with the butter as it foams.
Pour over the sauce, reduce the heat to low and a lid, then cook gently for 25 minutes.
Remove the lid and cook for a further 20 minutes to allow the sauce to reduce a little.