Start by conditioning your clay.  I do this by kneading small portions, as shown here.

In addition you can use a pasta roller like the one shown below. Once used for polymer clay don't use it for food again.

Combine all the small portions of the conditioned clay into a ball.  It is important that they are fully combined without air pockets.

To do this I forcefully roll them into a ball for several minutes.

Next use a roller to flatten the ball just a little.

Place two 6" - 8" long 1/4" dowels next to the clay as shown here.

Place your roller on top of the dowels as shown and flatten the clay. The two dowels will act as a bridge and give you a fairly consistent 1/4" thickness throughout the clay.

Don't worry about too much ends as these wont be used.

Press you cutter into the stock as shown here.

With the cutter still in-place, peel away the excess clay.

Remove the cutter.

Move the clay cutout to a tile as shown here.

As an option you can form and cut the clay directly on the tile.

Place your tiles in the oven.  Here I am going to bake four cutouts.

The toaster oven I am using is very accurate.  It will maintain temperatures within a couple degrees.

Bake for 1 hour at 280 degrees.