If you want to turn the Panna Cotta out onto a plate when set, first start by spraying your dariole moulds or ramekins with oil spray (I find metal dariole moulds easier to use). Wipe them with paper towel so there is only a light covering.
Pour 1 cup of cold milk into a saucepan and add the teabags, cinnamon stick, cloves, ginger and allspice. Sit over low heat swirling the pan every so often, until the milk is steaming and bubbles start appearing around the edge. Turn off the heat.
Cover saucepan and allow the flavours to infuse for 15 minutes. Then strain the mixture, making sure to squeeze the teabags well.
Rinse out the saucepan and add the final 3/4 cup of cold milk. Sprinkle the gelatine over the top. Allow the gelatine to "bloom" for 5 minutes (it should look a bit wrinkly by the end).
Turn the heat on low under the saucepan, add back the chai infused milk and stir for a minute or two until the gelatine has dissolved.
Add the sugar and stir again until dissolved. This should only take another minute or two. Make sure not to let the milk boil, you just want to heat it gently until everything is dissolved and no lumps remain.
Take the saucepan off the heat. Pour in the cream, vanilla and salt and mix until thoroughly combined. Strain the mixture again to make sure you aren’t left with any lumps of undissolved gelatine.
Pour into dishes or moulds. Place immediately in the fridge and allow to set for at least 4 hours (or they can be made a day ahead). See notes to unmould.