This concrete stepping stones recipe is an excellent choice for when you want a really smooth result.
In addition, this recipe is carvable, so if you want to add a design to the stone (such as the example pictured above), or maybe you just would like to carve your signature, or add a saying of some sort onto the surface, then I’d say give this easy stepping stones recipe a try. 
Before you get going, please make sure you’ve read over the Concrete Safety Guidelines and that you understand about the Curing How-Tos. (The curing information applies to both hypertufa and concrete garden art projects.)
Smooth Concrete Stepping Stone Recipe
1 part portland cement (sifted)
3 parts fine sand (sifted)
Optional: Concrete dye colorants
Enough water to make a mud-pie consistency
MATERIALS NEEDED:
A form or mold of some sort with REMOVEABLE SIDES;
Carving tools (spoons, screwdrivers, etc. work fine);
Bucket for water; old sponge to wipe off surface of stone.
**You might want to use white portland cement if you want a colored stone. Regular portland is grey, so of course this affects the final outcome of whatever colorant you may choose to use. However, white portland cement can be harder to find, depending upon where you live.
Make sure you’ve read this information on how to properly mix the ingredients. As with any concrete project, a successful outcome when mixing up this stepping stone recipe is dependent upon the proper ratio of ingredients: Mixing Guidelines: Tips to Help You Avoid Unnecessary Mistakes
As far as combining the three ingredients, as I’ve noted sifting the portland cement and the sand is recommended IF you desire a super smooth result. Otherwise measure out the portland cement and sand in the ratios given and break up any lumps with your gloved hands.
Then … slowly add in some water; mix and stir (or blend it in with your gloved hands). Keep adding a little bit of water, mix it in, and add a little more until your have the mid-pie, or some like to say “peanut butter”, consistency.
How To Make Your Stepping Stone
Step-By-Step Instructions For A Successful Outcome
#1) Ok, your mixture is ready! Now you can fill your form. Add it in increments, patting it down with your hands as you go along. You want to do your best to remove trapped air bubbles. Keep going until you have completely filled it up to the height you desire.
Also, many people pick up the edge of their form a few inches, and let it drop down onto the work surface, whereby helping to bring any other air bubbles up to the surface. This is just another way to “tap-tap” out the bubbles.
#2) Note: at this point there will be some excess water starting to collect on the surface. That’s OK … this is what is supposed to happen. (You’re doing great!)
#3) Using your gloved hands or a trowel, or if you are more particular a long stick to pull across the top … smooth the surface of your stepping stone.
#4) Let your stone cure. You do not cover the surface with plastic. It will take at least three (3) hours, probably closer to six (6) hours to cure enough before you can remove the sides of the form. Once hard enough (cured), you may carefully remove the sides of your form.