This photo shows a concrete countertop after the pour. The top is upside down, which is the way it must be poured to make a smooth top.
The top is leveled to within 1/16 inch, then a melamine sheet is laid on the surface. Next the template is laid on the melamine and 2 inch borders are screwed into the melamine around the edges of the template. This makes for a 2" thick top.
Rebar and wire mesh are added as needed. Finally the concrete is mixed and poured. My notes for mixing the concrete are here as a PDF download.
The top can be removed from the mold after four days. After 5 days the top can be surfaced with a 50 grit diamond wheel to expose pinholes and defects. Defects can be filled with a slurry mixture.
Be careful, it will take 10 - 14 days before the top is cured enough for a final polish.
If you are interested in something like this as a do-it-yourself project, you are welcome to contact me for more information. The Cheng Concrete Exchange is also an excellent resource for information and supplies.