First, cut the peaches in half and remove the stones, then cut the fruit in half again, lengthways. Place the quartered peaches in a saucepan with the caster sugar, the water and the lemon juice on a medium heat, and stir as it comes to the boil. Simmer for about 10 minutes, until the peaches are soft all the way through, but not falling apart.
Once cooked, remove the peaches from the poaching syrup. Peel the peach pieces and discard the skins. Put two peach quarters in each individual serving glass or bowl (little glass bowls look better).
In a small bowl, mix together the gelatine powder with 50ml (2fl oz) of water, place it in the fridge for five minutes to sponge, then tip it out and stir it into the hot syrup, heating the syrup a little more - if the syrup is hot enough, the gelatine should dissolve. Take the saucepan off the heat, then pour over the peaches in the serving bowls. Allow the desserts to cool, before placing them in the fridge to set. This should take a couple of hours.
Sprinkle with the borage or thyme flowers, if you're using them, and serve these on their own, or with ice cream or fresh cream, whichever you're using.