Clay : Baking Soda tecnique's tutorial
Original tutorial (wich uses paint thinners instead of Liquid Fimo/TLS) can be found here.
My tutorial is based on a different 'recipe', shared by Deviant Art' Shacchan.
You can read Shacchan's take on the tecnique at the bottom of this page :D
Roll Cake Charm Tutorial

Shacchan's instruction:
"First I got translucent liquid sculpey and mixed it together with regular sculpey
(kinda like when you make frosting, but it has to be thinner. Like a glaze.), and added a little bit of water to thin it out more and (in my mind) create more moisture for the baking powder to move around.

Then I got a small amount of baking powder and mixed it in with the "batter."
I haven't really calculated how much to add with what (because I forgot to write it down, like an idiot) so I would say play around with making about two tablespoons of batter and mixing in about 1/4 teaspoon of baking powder (or more or less depending) and just experiment with whatever works. I found that the less you put, you'll get a good texture for making little things like cheese cake textures or brownie textures, or even regular old cake, like in the link I gave you.

As for the "pan" I baked it in, I didn't have foam to wrap aluminum foil around, so I used the bottom half of a salt shaker and shaped a round pan with aluminum foil around it. You could use other objects too.

Then I baked it at the usual time sculpey or anything needs to be baked at, dusted the top with pastel dust (paintbrush or q-tip is fine) to try giving it a more realistic baked look, and prayed to God it looked like bread when I cut it in half, and it did!"