I've been steaming over this for a bit now, and I can come up with nothing other than:
A Cow pie; that being the pile of dung left by a cow, as well as a chocolately sweet (I'm familiar with the packaged candy from Baraboo, WI, but it also appears that there are "no-bake" cow pie/pile/patty recipes which popped after just searching those name variants).
I'm quick, I'm easy
No bake recipes are often less time consuming and involved, since no cooking is needed. It goes without saying that it's very easy for cows to make their pies.
You can make me in a jiffy
Again, with no time in the oven, those patties would be done in the time it takes them to set.
I'm on a farm
I'm in your kitchen
I'm in the pasture
Cows are on farms and roam the pastures, so this is where they leave their pies (Definitely Wisconsin...). And the kitchen is where you would make the confectionery variety.
I lay, I rot, in more places than one
Fields can be littered with pies.
I'm smelly, but I'm also very tasty
The cow's version is smelly, the chocolate is tasty.
I have nicknames but I prefer one
The origin is cow dung, but the cows' presentation of the dung likens it to a pie, a patty, or a pile (plus cow chips), which lead to us humans wanting chocolate in the same appetizing aesthetic. Lots of nicknames, but I think cow pie is most common.
What am I?
A cow pie/patty/pile/chip etc., of which the edible variety is a no bake treat, as the title hints. (The cow variety could be baked by the sun and then burned by settlers, but that's neither here nor there)