I already have a tutorial on making a wooden tray. It is very convenient and I use it every day. But I have decided to go ahead and make a concrete tray. Note that I make it not for any utilitarian reasons, but for the sake of aesthetic effect, so to speak. This is primarily a decorative element that attracts attention by its unusual shape and choice of material.
The most important thing is to let the tray dry properly! I removed cardboard after 24 hours, so that the tray dries evenly on all sides.
When grinding, you can wash the tray.