Can you buy clarified butter at the supermarket?

yes . Its in any international grocery or if you know or frequent a restaurant ask them to order you a Mid-America Farms tub of what they call "butter oil" . It's very fresh high quality ghee, or clarified butter at a reasonable price. The most common grocery store brand sold across the USA is Laksmi or Deep foods brands- you MUST check the date or open the jar as many are rancid from poor storage and shipping. . In the international isle at grocers or on the cooking oils or health foods isles you may also find it. As I said Mid-America farms is the best available and you may be able to order it direct or from an on line shopping site- unles you know someone in WI or IL the two plants it comes from .Sysco, Monarch and Nugget restaurant suppliers distribute it as well as food brokers ( to restaurant suppliers and bakeries). It comes in a single 4-5 lb tub for about 14 dollars and a four-pack of the tubs. It can be kept unrefrigerated for months in a cool dry environment. If you take some out for daily use, store in a covered jar near your gas stove so it stays liquid. it does however rapidly liquify.
If you make your own, begin with unsalted butter, at least 1 lb. put in a heavy saucepan and on a low fire, leave undisturbed - DO NOT STIR- for about 30 min. per lb. the protein solids will collect on tyhe bottom. If you have only salted butter, you must skim the salts which rise to the top off with a metal spoon .They can be collected and used in baking recipes and any sauce or gravy or tossed into sateamed veggies( adding no aditional salt). After the protein solids begin to turn golden pour off the ghee/clarified buter gently so as not to disturb the bottom of the pot.

If you desire a browned butter taste, allow the solids to go a shade or tow beyond golden- you will smell a nutty scent at which time remove fromo heat and pour off the clear liquid oil. It can be stored unrefrigerated if it absolutely clear- no solids or particles in the oil. After the first experimental pound of butter, it is best to use 5 lbs of unsalted butter to begin with as that will yield at least 3lbs of butter oil/ghee clarified butter- whatever you wish to call it.. as one lb will yield about a half cup of ghee if you are lucky...
the protein solids are just browned casein which is good stired into cooked rice, vegetables, soups and as an ingredient in baking to yield a more tender crumb ...
if you have more questions you may feel free to email me however my response may take more than 32 hours, at best!