Pour casting concrete into rubber gloves, being carefully to remove air bubbles from fingers. Mould into position working fast before concrete sets. When set, peel of rubber gloves revealing your concrete planter.
Check out info on resin casting. You have a mold, mix the resin with a catalyst. Whatever is in the mold gets embedded in plastic. - This link doesn't include info, but it's a reminder to go check out more info on resin casting
have shapecrete already pressed down into a plastic lined bowl, level the top. Paint leaf and second bowl with oil and press down into the first bowl (maybe weight second bowl with water?) no instructions at click through but lots of ideas