Prepare the Moulds
The first thing to do is to prepare your moulds. We used standard plastic Easter eggs. We began by drilling a large-ish hole in the top of the egg. Do this for each egg. I used an old egg carton to hold my moulds while we worked, since eggs don't have a flat bottom and won't stand up on their own.
Once the small hole is drilled, spray both sides of the inside of the egg mould with baking spray, this will make it easier to get your egg out later.

Mix Cement
Once your moulds are prepped the next step is to mix up your cement, making sure to stir it well so it’s fully combined, and always work in a well ventilated area. You want your cement mixture to be not too dry, and not too wet of a consistency. If it's too dry add a some extra water a little bit at a time. If it's too much water it will be a goopy mess, so add some more cement mix to make it dryer.

Fill The Eggs
To fill your eggs start by filling each side of the mould separately, and then try to snap the bottom of the egg and the top of the top of the egg together.  Working with the pointy end of the egg with the hole in the top, gently tap your full egg on a hard surface to try and get any air bubbles out of the cement mix.  Now if there’s any room at the top, use a plastic spoon to next pour a little more cement through the hole.  I also used a lollipop stick to push some more in the small opening at the top, and tapped it down.

Un-Moulding
Now leave your full concrete Easter eggs to set overnight. Overnight seemed to be a good length of time. You want your cement to be set, but not set too hard yet. Once your cement is set it’s time to take them out of the plastic container moulds.
This was the hardest part of the job.
A few came out easily, others were a little more tricky. Usually when you’re opening these eggs, you squeeze it a little to pop it open, but when it’s full of dry cement you can’t squeeze it. I used a knife in the crack and pried them open. Two of the plastic egg moulds broke as I was removing them. I did get all six of mine out, and they all turned out great, it just took a little elbow grease for some.

Sand and Smooth
Once the eggs are out of the moulds, you might want to use a little sandpaper or the edge of a knife to smooth out the bumpy surface where the egg shape clicked together. After a day of setting in the moulds the cement will still be soft enough when you take them out to scrap it smooth quite easily.