For 1 tile:

leftover ceramic tile pieces
1 plastic flower pot tray
chicken wire (cut to match the size of the bottom of the tray)
self-adhesive paper (cut to match the size of the bottom of the tray)
dry concrete
water
a bucket

Arrange the pieces of tiles on the bottom of the tray to your liking. Cover with the self-adhesive paper (let it stick to the top part of the ceramic pieces).
Carefully turn upside down and return to the tray with the paper on the bottom.
Combine the concrete with water in the bucket until it thickens but still has a liquid-like consistency. Pour a small amount over the ceramic and top with the wire.
Pour the concrete up to the top of the tray.
Shake to set and leave in a shady place to dry for at least 24 hours, sprinkling with water 1-2 times while drying.
When completely dry, turn upside down, remove the paper (if needed, scrape off any excess concrete from the tile using a small spatula), wipe with a dry cloth and place in the garden.