How to achieve a good steak crust with a blowtorch

I've come across two great, and very different, types of steak. The first is typical in Argentina and is not aged at all, but from a young calf (6-10 months old), free ranging and grass fed (hence not like classic veal). This is really juicy, tender, and with a very "bright" taste. Good high-end Argentine restaurants usually serve meat like this, and in the UK you can order it from pampasplains.com, which I think is great.

The second is from an older cow and dry aged to tenderize, but the aging also gives it a deeper, more bone marrow-like flavour. The best I've had of this type was a cow from Limousin in France, served in Paris at a small restaurant called Le Sèvero (8 rue des Plantes, 14th Arrondissment, reviewed in the NY Times a while ago). It was amazing! In London, 32 Great Queen St's "Hereford beef" is a similar style and also excellent. They get it from a Hereford farmer called Tom Jones (seriously), who serves several restaurants.

Good steak should never be marinated in anything - all it needs before cooking is salt, maybe pepper if you like (though I sometimes eat it with Coleman's English mustard).

I'm fairly sure that grass-only feed is important to good meat, i.e. no cereal-based fattening-up, though it's hard to separately test this one variable. Breed also clearly matters (all Argentine beef seems to be Aberdeen Angus or Hereford). I love a nicely marbled, fatty steak like the ribeye, but my (Argentine) wife prefers leaner cuts like sirloin and filet - clearly a matter of taste.

It sounds like you may be searing the steak for too long. Indeed, you want to initially be cooking the steak at a higher-than-normal temperature in order to sear it, but I'd suggest a period of more like 30 seconds each side, followed by slightly longer at a reduce temperature. At 650 degrees, the steak does not need long to sear. The same principle has worked for me when pan-frying steak, though obviously at much lower temperatures.

I'm not sure how large a role the salting is playing, but I would only salt the steak minimally before cooking. It's often just as well done towards the end of cooking, and is less likely to dry out the steak.

In addition, a common mistake is to pat down the steaks too much while (or after) cooking them. This may speed up the process slightly, but it certainly dries out the meat (the outside in particular). This is probably not the main problem, but is worth noting anyway.

Hope that helps.