2 off M4 nuts and bolts (10mm should do) are required for this print, as well as rapid setting cement.
I used Wickes rapid setting cement in this project. https://www.wickes.co.uk/Wickes-Rapid-Setting-Ready-Mixed-Cement---2-5kg/p/154061
Print in any material.

Creality

Ender 3

No

No

200

20

Can print in PLA - it doesn't matter really what filament you use.
Print two of the model, as each of them form a half.

Attach the halves together using the previously prepared two M4x10mm bolts and M4 nuts (washers can be used if you wish to use the mold many times). Do not over-tighten the bolts as this will damage the mold.

Mix rapid setting concrete and immediately pour in slowly.
I used Wickes rapid setting cement in my mold, following the suggested cement-water ratio on the instructions.
(https://www.wickes.co.uk/Wickes-Rapid-Setting-Ready-Mixed-Cement---2-5kg/p/154061)

For long life, add some fibrous material to ensure the concrete remains strong in tension.
Something like this should do:
https://www.wickes.co.uk/Sika-Cim-No-Crack-Concrete-Admixture-75g/p/154064

You can use a ruler/concrete trowel to level off the top.

I waited approx 40 minutes before removal, taking extreme care to not damage the concrete.
Do not wait too long as the model will affix itself to the concrete, and do not remove too early as the concrete will not be strong enough.

There will be some flashing along the edges, but this should be soft enough to remove with a ruler.
From here, place in a warm area and wait a day for it to have maximum strength.

I added cork pads to the bottom of my coasters to prevent scratching on surfaces. I washed the concrete beforehand to remove any residual dust.

And that should be it!