I’ve made numerous plates like this. They are a great size and shape for pie and small sandwiches. You have to really take your time to keep them from getting warped or cracked, but when they work, you have a set of matched almost-stacking plates.
To start with, you need a half dozen blemish-free styrofoam meat trays. The butcher at the local grocery store gave me some for the asking. If they have creases in them, they won’t work, because the creases will show up on your plate.
Roll out a slab on a slab roller, rotating ninety degrees with every pass, until you have about 1/4 inch thickness. Lay the meat tray with the convex side up on the slab and cut around the outside. Flip it over and gently lay the slab in so that the edges match. Gently press in the corners with your fingers.
Take a sharp, clean knife and trim the edges by holding the knife horizontally and cutting in one smooth pass all the way around the edge. Try not to nick the meat tray, so you can use it again. The less you touch the plate, the better it will look.
Let the plate dry very slowly, especially if you’re using porcelain. When it’s leather hard, flip it out of the tray and gently sand the edges. If your plate has alligator-skin cracks in the corners, the slab was too dry to start with.
