Try to place the ice mould at the top of the container. Place them like the photo below on top of a plastic cup. Ice will be formed from pure water. Therefore, we would like to make to freeze from the top so that air and impurities will go down. Preferably, the hole is more than 6 mm. If the hole is too small, you may get white parts in the ice. Therefore, the mould in the second photo below will get a better result than the last mould. You could make a bigger hole.

Wrap the Tupperware with bubble wrap so that it will get the cold air only from the top and will start to freeze from the top and not from bottom or side.

You could use a product like this as well. It has Then, you do not have to use bubble wrap. You could buy it at: https://amzn.to/3itq3Nt

Leave it at least 24 hours in freezer upto 30 hours until it freezes.

Remove the tupperware from the freezer and done! You can see how to remove the ice in the videos at: https://www.instagram.com/p/CCMV-2gn5u7/?utm_source=ig_web_copy_link

Enjoy slow melting crystal clear ice with your drinks.