I don't mean to be flip, but is there more than one? I mean, there's the S&W 340, which is under two inches of barrel and 12.5 oz.
Then there's the Ruger SP101 which, I'm sure, is a great gun, and lots of people seem to love them; but it weighs exactly twice as much as the 340. I know there are a few people who carry them in a pocket, but I also know there are a lot who've tried it and found them too heavy.
Then there's something by Taurus, I expect. Yeah.
Be aware that your question is going to get a lot of people responding that the Scandium 340 is too light for a 357. That's fine for them; I happen to think it's a fantastic little gun, and pocket carry mine just about every day. And yes, I shoot it. And yes, it hurt the first few times, and then I learned how to shoot it, and do so fairly regularly without undue discomfort. It's not a fun gun to shoot 2 or 3 boxes out of; don't make it your only gun. But what it does, it does incomparably well--put 5x357 in your pocket.
Many times you'll hear 'I wouldn't want to shoot anything more than .38 +P out of a little gun like that!' Okay, then do a quick search to find out how many threads there are fretting about the inadequate performance of 38+P ammo in snubnosed guns. The 340 solves that problem cold. It has its quirks, yes, and you should be aware of them going in. But, bottom line, the 340 is the only answer to your question.