If this is for a pathway my DH usually dig a hole in the size and shape of the leaf and about 2"to 2 1/2" deep, (we have sandy soil). For a nice even shape we put strips of cardboard around the inside - edges of the hole, and laid a few pieces in the bottom also, pour the mixed cement in and add the leaf, patting it onto the wet cement,(vein side down of course) completely cover with plastic. I then usually put a few small pebbles or sand on the top to keep the leaf as flat as possible, this is an almost one-step process, and the EE stones always turn out looking nice. On the other hand during the winter months we did try the other method using a wooden box on my craft table and used strips of heavy plastic to hold the cement edges firm. As you can imagine these big leaves can be very heavy to carry once turned to "stone". Good luck

Elephantear...do you have any pictures of what you are describing?? I am new here and trying to get as informed as possible before attempting a project.
Thanks!

Sorry,I didn't think at the time to take any pics. but I would think if just do a "trial run" (not adding the mix) following my instruction above you will find it's quite easy to do.
Unless you have rain you will need to keep the SS misted for approx. seven days. Wendy

I'm assuming you want leaf shaped and not square with a leaf imprint. Could you make a mold, pour in the crete, press in the leaf and when it's set enough to hold shape cut the excess away from the edges?