Han Solo in carbonite chocolate bar!

Step 1 Building your box mold.

You have to build a box around your object out of foamcore.

Or even cooler you can use your old Legos to make a box mold.
Here is a link with the basics.

http://www.starshipmodeler.com/basics/jc_molds.htm

I however had my Legos maliciously taken away from me at a very early age so I'll be using foamcore.

First using your glue-gun, glue your object to be molded onto a flat foam core peice. You want to create a seal all around the base of the object so silicone does not flow under the object.

Using the glue gun then glue a box around the object leaving a quarter of an inch to a half inch all the way around. This will make the mold strong and less prone to warping.

The particular food grade silicone, the Smooth sil 940 is easy to mix. I just poured the complete bottle into the silicone tub.
However each silicone is different. Double check your silicones instructions.

'Pouring silicone'
You're going to pour in your silicone. Best way is to start at a corner and let the silicone flow in/onto the mold and not pour directly on the mold. This helps reduce bubbles.

Let it cure for 24 hours then you remove the cured silicone from the foamcore box mold.

It's going to need post curing in a oven but use the instructions for your specific silicone product.