In Japan there has been a fad for a while for "sweets jewelry" (basically jewelry and related accessories that are made to look like realistic mini desserts). The jewelry can be bought readymade, but as part of the larger trend for decoden (basically, gluing rhinestones and/or little plastic cute stuff to cellphones, fake nails, etc.) it's also a popular craft-hobby.
The local lolitas do a monthly crafting meet-up and when it was my turn to host, I got a kit with some molds to make base shapes (a sort of tart shell and a rectangular cookie), 2 kinds of clay (resin clay and paper clay, both air dry) and a bunch of little plastic decorations (bows, flowers, animals, etc.) from some etsy sellers. For the faux whipped cream, I got a non-toxic silicone caulk. It seemed pretty fun but I was too busy hostessing to make more than one, and of that one, I made a sad gloopy little mess.
More recently I heard about a special craft-specific Japanese faux whipped cream. It's also silicone but supposedly less toxic than even the "non-toxic" caulk (since they don't really intend for you to be wearing/touching the caulk). It comes in a piping bag and can take piping tips, so I decided to try again, figuring I would have better control and less gloop.
The above photo shows the result of playing with it for a little while this evening. I made the tart-shape bases myself with the aforementioned kit, but it's the least interesting part of the process to me, so I think I will use more pre-made bases in the future, like the macarons (which I bought in a lot from yahoo-japan). My plan was to sell at least some of what I made (I don't need 4387 macaron rings), but while they are much improved from my first attempt, I'm not sure they are quite up to snuff. It is fun though, and I think I will get better with practice... hmm, an excuse to play with some real frosting, perhaps?