What can I use instead of butter for Jamie Oliver's steak recipe?

The butter is there for flavor, mouth feel, and to add some body to the sauce you make. I'd replace the butter with.... nothing at all. Many of the flavor compounds in garlic and rosemary are fat soluble and fat is not exactly in short supply when it comes to steak, so you should be able to run those on directly and still get some flavor. Alternatively you could steep some olive oil with the garlic and rosemary and brush a bit on, but I would just simmer them in the juices for a minute instead and then spoon them on the cooked steak.

I have a few comment's on Jamie's recipe:

1. Do not use olive oil when frying steak, it has too low a smoke point and may turn bitter. Use vegetable oil (canola/rapeseed, corn, peanut, sunflower, safflower, or blend) instead.
2. Do not pepper the steak before frying as pepper will burn and turn bitter. Add fresh pepper just after you remove it from the pan to rest. If you want a pepper flavor inside the steak use a marinade. Salting before is fine
3. The oil is not a seasoning, that's the salt and pepper. The oil's purpose is to help conduct the heat from the pan to the steak until the steak's juices come out
4. There flip repeatedly method works but it isn't the only way to do it, I prefer to flip once after about 65% of the cooking time has elapsed. Doing a 65-35 rather than a 50-50 flip will make your steak evenly pink in the middle and means you can turn your attention to other things. I also think you get a better sear when using a pan. I use the 1 minute flip over charcoal though as it keeps the steak from getting too crispy

The only effects of rubbing a bit of butter on the steak in the middle of frying it I can think of are:

• Add a hint of buttery flavour.
• Provide more fat to help keep the steak from sticking to the pan.
• Salt the steak a tiny bit, assuming you used salted butter.

I think only the second effect would be important enough to make it worthwhile find a substitute for. Rubbing the steak with some more olive oil, dairy-free margarine or even just spraying with cooking spray, should work as a substitute. However you can probably get away with not doing anything to replace the butter. In addition to the oil you've already seasoned the steak with, fat rendered from the steak itself should keep it from sticking. If you find it sticks anyways, then next time you can rub on some more oil.

I don't think it would be worthwhile to find some non-dairy substitute for the flavour of the butter. If you think the steak is going to miss that bit of salt the butter provides, I would just add a dash of salt to the juices you're using as a sauce.

If you don't want to use dairy then don't. However, butter on a steak has very distinct flavor a feel effects. There is no substitute to replace this.

You could try ghee / unclarified butter. You can make it pretty easily with unsalted butter, which will remove the dairy solids, or you can buy it at Trader Joe's, online and at many grocery stores, including Walmart (look in the Ethnic foods section with Indian products).

I think you could just do without the butter. It does add a certain enhancement to the steak, but nothing that will be missed too badly. You may want to grill the steak for better flavor (that's just my opinion) instead of frying it--and you will easily do without the butter.

I found this recipe online, which seems closest to the Jamie Oliver recipe you mention in brief. The only divergence is no mention of turning the steak over regularly, and I agree with @GdD's method. http://www.precisionnutrition.com/the-perfect-steak

Coconut oil is similar smoke point to butter, so that will help sear the steak with a slightly different flavour. Avocado oil has an even higher smoke point, so is another good substitute.

However, you might want to try beef tallow or similar? You can get the temperature much higher.

Some people say get the steak to room temperature, whilst others say freeze it first. I am going to try the latter method next time (but only when using a meat thermometer!!)

Finally, where your steak comes from and cut will make the most difference, so pay a bit extra and go to a butchers or choose a better cut. I prefer fattier steaks, my wife prefers prime, so we just buy one of each and everyone is happy.