I made my own moulds to make raspberries and blackberries. There really isn't any other way to make these berries. It would be way too tedious to do them by hand! First, I made the master berries from tiny glass microbeads glued onto a toothpick. I put those into silicone rubber putty, and once hardened, it makes superb polymer clay raspberries. I have written a blog post on exactly how I use them.
I use liquid clay to fill the cavities. This does cause bubbles to get trapped, but with enough patience, I can get most air bubbles out by gently poking and prodding with a toothpick. Once they are all filled, I bake the mould together with clay at 110 degrees C for 30 mins. I have not tried this with clays that bake at higher temperatures, but for Fimo, the mould survives very well and can be used over and over.
I also use various other flexible silicone moulds to make cupcake bottoms and pie bottoms. They are really necessary to make cupcake bottoms that look even, with a good pattern. I tried sculpting these by hand, but it never worked. I also bake these together with clay in the oven, and this ensures that I never distort the shape.
To make this cupcake, I bake in several stages. First, the cupcake base inside the mould. Then, I put the cupcake top on, and bake again, and finally, I decorate the cupcake with icing and sprinkles.